Frequentists vs. Bayesians

Explanation:
This comic is a joke about jumping to conclusions based on a simplistic understanding of probability. The " base rate fallacy " is a mistake where an unlikely explanation is dismissed, even though the alternative is even less likely. In the comic, a device tests for the (highly unlikely) event that the sun has exploded. A degree of random error is introduced, by rolling two dice and lying if the result is double sixes. Double sixes are unlikely (1 in 36, or about 3% likely), so the statistician on the left dismisses it. The statistician on the right has (we assume) correctly reasoned that the sun exploding is far more unlikely, and so is willing to stake money on his interpretation.
The labels given to the two statisticians, in their panels and in the comic's title, are not particularly fair or accurate, a fact which Randall has acknowledged: [1]
The " frequentist " statistician is (mis)applying the common standard of " p <0.05". In a scientific study, a result is presumed to provide strong evidence if, given that the null hypothesis , a default position that the observations are unrelated (in this case, that the sun has not gone nova), there is less than a 5% chance that the result was merely random. (The null hypothesis was also referenced in 892: Null Hypothesis .)
Since the likelihood of rolling double sixes is below this 5% threshold, the "frequentist" decides (by this rule of thumb) to accept the detector's output as correct. The " Bayesian " statistician has, instead, applied at least a small measure of probabilistic reasoning ( Bayesian inference ) to determine that the unlikeliness of the detector lying is greatly outweighed by the unlikeliness of the sun exploding. Therefore, he concludes that the sun has not exploded and the detector is lying.
A real statistician (frequentist or Bayesian) would probably demand a lower p -value before concluding that a test shows the Sun has exploded; physicists tend to use 5 sigma, or about 1 in 3.5 million, as the standard before declaring major results, like discovering new particles.  This would be equivalent to rolling between eight and nine dice and getting all sixes, although this is still not "very good" compared to the actual expected likelihood of the Sun spontaneously going nova, as discussed below.
The line, "Bet you $50 it hasn't", is a reference to the approach of a leading Bayesian scholar, Bruno de Finetti , who made extensive use of bets in his examples and thought experiments. See Coherence (philosophical gambling strategy) for more information on his work. In this case, however, the bet is also a joke because we would all be dead if the sun exploded.  If the Bayesian wins the bet, he gets money, and if he loses, they'll both be dead before money can be paid. This underlines the absurdity of the premise and emphasizes the need to consider context when examining probability.
It is also possible that the use of the sun is a reference to Laplace's Sunrise problem .
The title text refers to a classic series of logic puzzles known as Knights and Knaves , where there are two guards in front of two exit doors, one of which is real and the other leads to death. One guard is a liar and the other tells the truth. The visitor doesn't know which is which, and is allowed to ask one question to one guard. The solution is to ask either guard what the other one would say is the real exit, then choose the opposite. Two such guards were featured in the 1986 Jim Henson movie Labyrinth , hence the mention of "A LABYRINTH GUARD" here. A labyrinth was also mentioned in 246: Labyrinth Puzzle .
As mentioned, this is an instance of the base rate fallacy . If we treat the "truth or lie" setup as simply modelling an inaccurate test, then it is also specifically an illustration of the false positive paradox : A test that is rarely wrong, but which tests for an event that is even rarer, will be more often wrong than right when it says that the event has occurred.
The test, in this case, is a neutrino detector. It relies on the fact that neutrinos can pass through the earth, so a neutrino detector would detect neutrinos from the sun at all times, day and night. The detector is stated to give false results ("lie") 1/36th of the time.
There is no record of any star ever spontaneously exploding—they always show signs of deterioration long before their explosion—so the probability is near zero. For the sake of a number, though, consider that the sun's estimated lifespan is 10 billion years. Let's say the test is run every hour, twelve hours a day (at night time). This gives us a probability of the Sun exploding at one in 4.38×10 -13 . Assuming this detector is otherwise reliable, when the detector reports a solar explosion, there are two possibilities:
Clearly the sun exploding is not the most likely option. Indeed, Bayes' theorem can be used to find the probability that the Sun has exploded, given a result of "yes" and the prior probability given above:

[Caption above the first panel:] Did the sun just explode? (It's night, so we're not sure)
[Two Cueball-like guys stand on either side of a small table with a small black device on it. The device has white lines (ventilation) and two small antennas and a button on top. When the device speaks it uses in Westminster typeface. The Guy on the left, called Frequentist Statistician in the 2nd panel, points to the device. The guy on the right, called Bayesian Statistician in the 3rd panel, is just looking at the device. Above the spoken word from the device is a sound.] Frequentist Statistician: This neutrino detector measures whether the sun has gone nova. Bayesian Statistician: Then, it rolls two dice. If they both come up as six, it lies to us. Otherwise, it tells the truth. Frequentist Statistician: Let's try. Detector! Has the sun gone nova? Sound: Roll Device: YES.
[Two panels side by side are beneath the first panel. together they are broader than the top panel. Above each panel is a caption. In the left panel only the left statistician is shown with the device on the table. And in the right panel only the right statistician is shown with the device on the table. both are just looking at the device.] Frequentist Statistician: Frequentist Statistician: The probability of this result happening by chance is 1/36=0.027.  Since p<0.05, I conclude that the sun has exploded.
Bayesian Statistician: Bayesian Statistician: Bet you $50 it hasn't.


Up Goer Five

Explanation:
This comic is an illustration that will later be used in Randall 's book ' Thing Explainer ', where he took it upon himself to explain a number of things, including the Saturn V rocket shown here, using only the one thousand most commonly-used words in the English language.
This comic is a diagram of the Saturn V rocket. "Saturn" isn't a very common word apparently, and neither is rocket, so Randall decided to use "Up Goer" which is a fair approximation of a craft designed to lift a payload from the earth to space, although perhaps 'thing that goes up fast' may or may not be simpler. The Saturn V vehicle, which was in use by NASA from 1967 to 1972, is the vehicle as a whole. The engines of the Saturn V (the part that makes it go up) were divided into three stages. The first stage ( S-IC ) had five F-1 engines which burned refined kerosene mixed with oxygen as its fuel. That stage burned for 2 minutes 48 seconds and pushed the whole thing up about 61 kilometers (~38 miles) into the sky. After it fell away the S-II stage was activated. It used 5 J-2 engines in the same configuration as the F-1s, and burned liquid hydrogen mixed with liquid oxygen for 6 minutes 35 seconds pushing the astronauts up to 184 kilometers (114.5 miles). The third stage ( S-IVB ) was a single J-2 engine burning liquid hydrogen and liquid oxygen. This stage was used in two parts, the first was to put the spacecraft into a stable orbit around Earth to perform a systems check and make sure the craft will be safe for going to the moon. This would usually take three orbits around Earth. As they came around the Earth they would burn the second part of the fuel, which is called a trans-lunar injection which put them on course for the moon. The first burn took 2 minutes 45 seconds, which put them in orbit 185 kilometers (115 miles) high.
It was first used as the launch vehicle for the Apollo 4 mission, and it was used as the launch vehicle for most of the subsequent Apollo missions (the exceptions being Apollo 7, Skylab 2-4, and the Apollo-Soyuz Test Project missions, which were launched using the smaller Saturn IB launch vehicle). One of the last missions of this design was the unmanned launch of Skylab , the U.S.'s first space station; for this payloader configuration, the Saturn V launch vehicle was officially designated the Saturn INT-21 .
The Service Module (SM) Oxygen tanks have a note that states "This part had a VERY big problem once". This is a reference to the Apollo 13 mission. 55 hours after launch, mission control requested the oxygen tanks contents be stirred to get an accurate reading of its contents. There was a large bang , and power fluctuated throughout the craft. NASA had to scramble to ensure the safe return of the astronauts. Needless to say, the moon landing for that mission was canceled.
The Hindenburg disaster is referenced in the text "The kind of air that once burned a big sky bag and people died and someone said "oh, the [humans]!". The term "big sky bag" is used as the closest approximation of zeppelin which is a big bag filled with a lighter-than-air gas which makes the whole contraption float. The phrase "oh, the [humans]" is a workaround of the simple-words rule, technically containing only the word humans, while being read "concentration of humans" or "humanity". The Hindenburg on the day of the disaster was filled with hydrogen , despite being initially designed for use with helium . Helium cannot catch fire as it is a noble gas and thus completely inert, but helium was unavailable due to a US export ban on the element. The risks seemed acceptable at the time because the Germans had a history of flying hydrogen-based passenger airships. The original quote is "Oh, the humanity!" (See this video about the Hindenburg disaster - the quote appears at 0:47). In the book Thing Explainer in the explanation for The pieces everything is made of (i.e. the Periodic table ) hydrogen is again "named" by using a picture of the burning Hindenburg and also this quote is said by Cueball standing next to the square with the element with his hands over his mouth. See more below regarding the book.
The bottom tank, which Randall describes as "...full of that stuff they burned in lights before houses had power" is highly refined kerosene, called RP-1 , it is similar to jet fuel, burns well and is not likely to explode; unlike liquid hydrogen , which is much more likely to explode.
Earlier flirts with simple words can be found in 547: Simple and 722: Computer Problems .  The use of simple words was revisited again in 1436: Orb Hammer and 1322: Winter .
The comic is based on NASA-MSFC 10M04574 produced at Marshal Space Flight Center. Randall omitted the "S".  The image was for sale as a poster from up-ship.com which Randal mentioned.  A different scan is downloadable from Heroic Relics .
The phrase "You will not go to space today" has become something of a catchphrase for xkcd — variants of it recur in the title text of images in four What If? articles:
Randall has in 2015 written an entire book with this type of simplified language blueprints. Thing Explainer was published by Houghton Mifflin Harcourt on November 24, 2015 and actually had a copy of this comic in it. On the day of the book's release Randall also released a comic with a game, to celebrate the book: 1608: Hoverboard . In this game the space capsule used for landing back on earth is shown, thus both referencing the book and this comic. This part of the space ship can also be seen in the book above the Sky toucher and the moon landing is also depicted in Worlds around the sun . When the book was released Randall had Minute Physics do a "commercial" version of this comic .
The news about the upcoming release of the book was sent out on the Blag in May as New book: Thing Explainer . After that, the book was advertised at the top of the xkcd page with link to the Blag article and links to Preorder at Amazon, Barnes & Noble, Indie Bound, and Hudson. Also, there were two other news with links: "In other news, Space Weird Thing is delightful , and I feel surprisingly invested in @xkcdbracket's results." (The link was removed sometimes before Monday the 10th of August 2015. within two weeks of the brackets final result was revealed.)
The song Space Weird Thing is a tribute to David Bowie 's Space Oddity rewritten in the simple language used in this comic, which is also attributed in the text about the YouTube video. The other news item is related to 1529: Bracket , see that comic for more details.
US Space Team's Up Goer Five The only flying space car that's taken anyone to another world (explained using only the ten hundred words people use the most often) [A list of Saturn-V parts, top to bottom, with their "Up Goer" description follows.] [Launch Escape System (LES)]: Thing to help people escape really fast if there's a problem and everything is on fire so they decide not to go to space [LES side nozzle]: Thing to control which direction the escaping people go [LES fuel]: Stuff to burn to make the box with the people in it escape really fast [LES bottom nozzles]: Place where fire comes out to help them escape [Apollo spacecraft.] [Command Module (CM)]: Part that flies around the other world and comes back home with the people in it and fall in the water. [CM capsule parts]: People box, door, chairs [Service Module (SM)]: Part that goes along to give people air, water, computers and stuff. It comes back home with them but burns up without landing. [SM oxygen tanks]: Cold air for burning (and breathing). This part had a VERY big problem once. [Lunar Module (LM)]: Part that flies down to the other world with two people inside [LM descent stage]: Part that stays on the other world (it's still there) [LM feet]: Feet that go on the ground of the other world [Instrument Unit]: Ring holding most of the computers [S-IVB third stage]: Part that falls off third (this part flew away from our world into space and hit the world we were going toward) [Fuel tanks]: Wet and very cold [Liquid hydrogen (LH2) tank]: The kind of air that once burned a big sky bag and people died and someone said "Oh, the [humans]!" (used for burning) [Liquid oxygen (LOX) tank]: The part of air you need to breathe, but not the other stuff (used for burning) [Helium pressurizing tanks]: Things holding that kind of air that makes your voice funny (it's for filling up the space left when they take the cold air out to burn it.) [J-2 engine nozzle]: Fire comes out here [S-II second stage]: Part that falls off second [LH2 tank]: More sky bag air (for burning) ( cold + wet) [LOX tank]: More breathing-type air (for burning) ( cold + wet) [Tank-to-engine fuel lines]: Thing that brings in cold wet air to burn [J-2 engine nozzles (qty. 5)]: Fire comes out here [S-IC first stage]: Part that falls off first [LOX tank]: More breathing-type air (for burning) ( cold + wet) [Helium pressurizing tank]: More funny voice air (for filling up space) [LOX fill line]: Opening for putting in cold wet air [RP-1 fuel tank]: This is full of that stuff they burned in lights before houses had power.It goes together with the cold air when it's time to start going up. [F-1 engine nozzles (qty. 5)]: Lots of fire comes out here. [Bottom of spacecraft]: This end should point toward the ground if you want to go to space. If it starts pointing toward space you are having a bad problem and you will not go to space today.


Logic Boat

Explanation:
The comic is a play on the classic wolf, goat and cabbage puzzle belonging to the river crossing puzzles , and first known from Propositiones ad Acuendos Juvenes , with the same setting as here. The three possessions change between various retellings but it typically involves a carnivorous animal (wolf, lion etc.), a herbivore (goat, sheep, chicken, goose etc.), and some plant based food (cabbage, grain, beans etc.). The objective is to ferry all three possessions to the other side of a river safely in a small boat , with the limitation of only being able to transport one possession per crossing. The crossing order must take into account that the carnivore would eat the herbivore if left alone together, and the herbivore would eat the food.
The traditional solution would be:
(Note that, since the conditions for this problem are symmetric, an alternate solution would be to transport the wolf on Trip 3 and the cabbage on Trip 5.)
By leaving the wolf behind, four steps are saved — the comic's "step 4" is just a comment — and the troublesome wolf, a wild and dangerous animal not usually kept by humans, is eliminated from the picture.
This could be seen a jab on the common assumption that logic puzzles only have one correct solution. Thus one often keeps the other person thinking and guessing until they arrive at the pre-defined solution, no matter how many other creative good solutions they come up with. Also note that the "problem" given doesn't even state an objective, just three prerequisites.
Alternatively, this could be a jab at the fact that the conditions of some puzzles are very strange. Both the fourth step and title text are evidence of this - questioning why you would have a wolf or a cabbage respectively. Yet, even though it is unlikely that you would ever find yourself in the situation and odd rules as stated by the puzzle in real life, [ citation needed ] the puzzle demands that you solve it and reach the criteria it asks.
The title text says that cabbages are also unnecessary, but goats are fine. The reasons for these opinions are less obvious than the one about the wolf, but still understandable. Many people, presumably including the narrator, do not like the taste of cabbage. Many are also fond of goats, finding them cute. The same opinion about goats is in 1282: Monty Hall .
The river crossing puzzle was the main focus of 2348: Boat Puzzle . It was referenced in 589: Designated Drivers .
[A person shows up at a boat docked at the edge of a river. The person has brought along a head of cabbage, a goat, and a wolf.] Problem: The boat only holds two, but you can't leave the goat with the cabbage or the wolf with the goat.
[The wolf looks curiously at the cabbage that's been left behind while the person goes off with the goat.] Solution: 1. Take the goat across.
[The goat remains tied up on the far side. The wolf watches the person come back.] 2. Return alone.
[The wolf sits and waits as the person goes off.] 3. Take the cabbage across.
4. Leave the wolf. Why did you have a wolf? [The wolf goes off.]


Arachnoneurology

Explanation:
Beret Guy uses spider psychology (that he has obviously learned from the heavy volume of a book lying on the table with that title) to engineer a forked object in such a way that spiders will weave a silk shirt around it. After six weeks he can take the finished shirt off the "rack", and after optionally removing some stray spiders it should be ready for use.
Usually extracting spider silk is a complicated process and getting enough to weave a shirt would take very long and be very expensive. But making such an impossible project work is a typical behavioral pattern for Beret Guy, who continues to do amazing things with animals and other things from nature.
The prefix arachno- means "(related to) spiders". Arachnology , for example, is the scientific study of spiders. Neurology is a branch of medicine dealing with disorders of the nervous system , which includes the brain . So the title of the comic can be translated into the scientific study of spider brains .
The title text mentions the book lying on the table, giving not only the title and the edition (21st) but also summing up some more (non-existent and increasingly far-fetched) fields of science related to spiders, which may as well exist if spider psychology has such a big standard work. Apart from adding the word forensic in one case, all five fields come from combining only the same two words "arachno" and "neuro" (sometimes one of them more than once) and ending any combination with "-ology". Especially funny is the neuro-arachnoneurology, which is explained to be the field where it is the brains of the scientist who study spiders brains, that are examined. The last one seems to be related to arachnophobia , the fear of spiders, as arachnoarachnology is spiders with spiders on top - i.e. too many spiders .
Arachnophobia seems to be a problem for Randall himself, according to the What if? Spiders vs. the Sun . In this he links to an article about a factory that was covered in plenty enough spider web silk to make shirts to a whole regiment of soldiers.
This is the first comic with special mentioning of a science related directly to spiders. The next was 1747: Spider Paleontology .
[Beret Guy holding a protractor and handling a fork-like stand with black knobbly protrusions. On the table is some sticks, a set square and a ruler. There is also a large book titled: Spider Psychology [Beret Guy places his creation in a cobwebbed corner.] [Spiders weave webs around Beret Guy's creation. One of them hangs down above it from the ceiling.] [Beret Guy pulls a shirt made of spider silk away from his creation. At the top of the panel is a frame that breaks the main panels frame. Inside this it says:] Six weeks later:


Broken Mirror

Explanation:
It is a common superstition that breaking a mirror will result in 7 years of bad luck. Black Hat mocks the superstition, claiming that all is random, but ultimately cause the superstition to become true as his nihilistic apathy prevents him believing that cleaning the glass on the floor will have a significant impact. The joke is that Black Hat will likely get glass in his feet as long as he refuses to clean it, and thus the broken mirror will have a lasting impact.
Black Hat breaks a mirror and sarcastically claims that it will bring bad luck for 7 years, implying that the broken mirror will have no impact on his life. After Cueball reminds Black Hat that the broken mirror will at least cause him to clean up the glass. Black Hat responds with a quote from Ecclesiastes that explains "being clean" (doing good) or "being unclean" (doing bad) things does not affect whether good or bad things happen to us. Due to Black Hat's interpretation of Ecclesiastes , he is not going to clean the shards, and thus be "unclean", and feels nihilistically that this will not significantly alter his life. Of course, it will have an impact as he will get glass in his feet if he does not clean it.
Black Hat continues saying that "My fate is as these shards" this mirrors another quote from Ecclesiastes "For what happens to the sons of men also happens to animals". Cueball tries to cheer up Black Hat by reminding him that life is not that bad, "it's just a vanity mirror". Black Hat responds saying, " All is vanity mirrors". "All is vanity" another quote from Ecclesiastes, this line is repeated throughout the book and refers to impermanence of man and his creations. As the mirror just broke, its impermanence is apparent.
It is possible that this is a reference to the now-defunct webcomic Men in Hats and its character Aram, specifically in this page . Aram has been described as the inspiration for Black Hat in 29: Hitler .
In the title text Cueball says  "I see you're in this mood again" to which Black Hat responds, "I am always in this mood". This is a reference to Black Hat being a nihilist in his other appearances.
Breaking mirrors is also mentioned in 2447: Hammer Incident .
The rejection of the idea that good things happen to good people, and therefore the rejections of concepts like karma, is one of the primary tenets of the Abrahamic faiths. The argument goes that if people deserve what happens to them, then they don't deserve help. This, and the pursuit of justice (fairness, and truth) are the core beliefs that prescribe that each person has an individual responsibility to help others, so that justice can be achieved. Since Black Hat is by no means charitable, this belief clearly never took root.
[Black Hat and Cueball stand in a bedroom. There is a broken mirror on the floor at Black Hat's feet.] Black Hat: Oops. Guess this means seven more years of the illusion that my actions somehow influence the indifferent hand of probability which governs our lives.
[Black Hat looks down at the broken shards of glass on the floor.]
Cueball: Plus like half an hour of sweeping. Black Hat: No, I think I'll leave it. Cueball: You'll get glass in your feet.
Black Hat: Eccles. 9:2—All things come alike to all: to the clean, and to the unclean. Black Hat: My fate is as these shards. Cueball: Dude, chill. It's just a vanity mirror. Black Hat: All is vanity mirrors.
Judging from the damage done to the wall and the way the mirror landed face up, it is likely that Black Hat intentionally broke the mirror.
The way Cueball and Black Hat appears and the subject has some similarities to the next comic 1137: RTL . See the trivia section for that comic.


RTL

Explanation:
U+202e is a unicode control character that changes all subsequent text to right-to-left (RTL, as the title references). In the comic, Black Hat tires of Cueball 's complaining and inserts a U+202e character in the middle of Cueball's speech, turning his complaints into gibberish - sentences that must be read from right-to-left.
The title of the comic builds on this theme, with the title of the webpage it is hosted on being LTR in some browsers (see trivia ), the reverse of the comic name.
What Cueball actually tries to say after Black Hat's change is:
— They didn't even... ...What the hell? How did you... ...Asshole.
When multiple writers work on the same text, arguments can often arise with some writers resorting to vandalizing the works of other writers. The title text takes this up a level, suggesting the use of U+202e and other direction control characters in editor wars to disrupt other people's work.
If you ever get involved in such a war, note that U+202c returns text back to its normal direction.
[Cueball is standing behind Black Hat who is sitting down with a laptop on his lap.] Cueball: And that's not even the worst part! The worst part is that— Black Hat types a command on the PC: U+202e Cueball: —They didn't even... Cueball: ...What the hell? Cueball: How did you... Cueball: ...Asshole.


Heatmap

Explanation:
Another of Randall's many Pet Peeves , this time on maps . This one has also been numbered #208, like the first comic on the subject 238: Pet Peeve #114 .
In the comic, Cueball compares three heatmaps, showing the location of "our site's users," "subscribers to Martha Stewart Living " and "consumers of furry pornography." The three maps are nearly identical, leading Cueball to come to the conclusion that his site's userbase largely consists of fans of Martha Stewart and furry porn, and that the audience (presumably the owners/operators of the website) should adjust their content or advertising to cater to these demographics. However, Cueball's analysis is faulty; the actual reason the maps are the same is they all match the population concentration in the U.S., not because there is any statistically-significant relation between geographic location and any of the mentioned sub-populations.
A heatmap is a graph showing three-dimensional data on a two-dimensional image, with each pixel's colour representing the value of the data at that position.  It does not necessarily have anything to do with heat, but a heatmap may resemble a thermal image.  In this comic, red represents the highest numerical values, then yellow and green, with white the lowest values, in all three maps.
The title text reflects a similar situation in world maps where the website written in English is read by English-speaking users no matter the location, because their ISP and search providers direct them primarily to English websites, so the visitors' geographic graph matches the graph of the global English-speaking population.
[Three near-identical charts of the 48 contiguous United States are shown with heatmaps depicting population density. The first chart is labelled "Our site's users," the second chart is labelled "Subscribers to Martha Stewart Living ," and the third chart is labelled "Consumers of furry pornography." Cueball is standing with a stick pointing at the charts.] Cueball: The business implications are clear. Pet peeve #208: Geographic profile maps which are basically just population maps


Rubber and Glue

Explanation:
"I'm rubber, you're glue; whatever you say bounces off me and sticks to you" is a school-ground retort used by children to suggest that one's insults are being ignored by the intended recipient of the insult and counter that the insult rather refers to the insulter . On a deeper level, it may imply that a person insulting others is an indication of their own insecurity and weakness.
In this comic, a young Black Hat is reading a chemistry and physics handbook, which leads to a literal and graphic visualization of the phrase. He uses the retort to frighten the children bullying him (young versions of Hairy and Cueball ). Black Hat takes the traditional saying and twists it into a creepy thought by saying that they are both literally glue and rubber and that they are permanently stuck together, which scares Hairy and Cueball and prompts them to call for their mothers.
The book is the CRC Handbook of Chemistry and Physics . It is also nicknamed the 'Rubber Bible' or the 'Rubber Book', as CRC originally stood for "Chemical Rubber Company".
The title text says that I (meaning him) and you (Hairy and Cueball, although it could possibly be the reader) are both rubber. Rubber is not a living object, so it is stuck in "vulcanized horror" in the position it was sculpted in. This could be a reference to how powerless we are in the changing of the world.
Young Black Hat also taunts young Hairy later in 1753: Thumb War .
[Playground. Young Megan is balancing on a swing, two Cueball-like kids are swinging and two more kids, a young Cueball and a young Hairy are approaching a reading young Black Hat, whose hat is almost too big for his small head.] Hairy: Whatchya reading, Hatboy? Black Hat: The CRC Handbook of Chemistry and Physics. Cueball: You are such a loser, it's painful . Black Hat: I'm rubber, you're glue.
[In a frame-less panel Hairy and Cueball looks down on Black Hat sitting with his book in his lap on the ground between them. He looks back up over his shoulder at Hairy.] Hairy: Yeah, well— Black Hat: Glue can't speak. Black Hat: You try to scream, but your mouth fills with glue. Black Hat: Your face is glue. Your body is glue.
[Black Hat has left the book on the ground behind him and has risen. Hairy and Cueball is now together to the right and Black Hat advances towards them arms stretched out. Hairy steps backwards away from him.] Black Hat: I wrap my rubber arms around your sticky bulk. Black Hat: Your neoprene base bonds instantly with my surface. Black Hat: Never to let go.
[Zoom in on Black Hat's head. He is holding his arms up in front of him clapping them together. Hairy shouts from off panel.] Black Hat: You are glue. I am rubber. Black Hat: Staring at you with my dead, rubber eyes- Black Hat: Forever. Hairy (off-panel): Moooom!


Calendar of Meaningful Dates

Explanation:
The calendar used in the comic is the standard Gregorian calendar used by most of Western Civilization. The comic looks at the frequencies of which dates appear in English writings indexed in the Google Books Library Project , by using the Google Ngram Viewer ( link ).
Some dates are more (or less) frequently mentioned because they have a special significance. Other dates have correlations for which there doesn't appear to be any obvious reasons. September 11th, which is noted in the title text for being popular before the 9/11 attack, has also been the date of 2 significant battles in the War of 1812, one where the British landed in what was George Washington's large plantation, which likely contributed to its search volume.
The date mentioned in the sub-heading (October 17th) is Randall's birthday.
The title text mystery is explained here . In summary, many occurrences of "11th" in the writings were actually misread by the Google Books Library Project's optical character recognition software and/or reCAPTCHA users, becoming one of these: IIth , Ilth , iith , lith , llth , 1lth , 1ith , l1th , nth .
The first of each month is generally more mentioned than others, perhaps because such dates are markers of a new month and may be used as landmark dates or deadlines. Similarly, the final day of each month is commonly a deadline day. Other dates have a less mundane significance, for example:
Calendar of Meaningful Dates Each date's size represents how often it is referred to by name (e.g. "October 17th") in English-language books since 2000 (Source: Google ngrams corpus) [A regular Gregorian calendar laid out in a grid, Sunday first, on a leap year, with some numbers larger than others.]


Two Years

Explanation:
This comic marks the second year of Randall Munroe 's wife's battle with cancer, and appears to depict actual events from those two years. Randall is depicted as Cueball and his wife as Megan , as usual for both.
This comic later became part of a series of comics directly continued in 1928: Seven Years and later continued in 2386: Ten Years . The first eight panels of this comic are included in the next two, although  slightly grayed out.
Explanations of the individual panels:
The title text is referring to a possible side-effect of chemotherapy drugs , the inability to concentrate. It could also just be the fact that the chemo can make you feel just terrible. When whatever effect kicks in, she loses the rest of their Scrabble games for that day. However, as we see in panel 5, there is a reason why she wins all of the first half of their games. But this is not enough, or she even forgets to play on the cancer, when the drugs take effect.
The use of the asterisk in the title text for "*dominated*" might be a reference to the 1999 game Unreal Tournament in which the game announcer voice would from time to time use the words "dominating" or "dominated" in a deep tone when a player is doing really well in the game (for example being on a multi-kill strike). Example sound here .
Knit caps have only been used a few times in xkcd, most prominently on Knit Cap Girl in 1350: Lorenz , see her section for more details.
[Randall and Randall's fiancée sit on a bed, Randall's fiancée is talking on the phone. The person she is talking to, a doctor holding a clipboard, is shown inset.] Randall's fiancée: Oh god.
[Randall and Randall's fiancée sit together while Randall's fiancée, now bald, is receiving chemotherapy. They are both on their laptops.] IV pump: ... Beeep ... Beeep ... Beeep ...
[Randall and Randall's fiancée (who is wearing a knit cap) are paddling a kayak against a scenic mountain backdrop.]
[Randall and Randall's fiancée sit at a table, staring at a cell phone. There is a clock on the wall. Her head is stubbly.] Randall's fiancée: How long can it take to read a scan!?
[Randall and Randall's fiancée are back at the hospital again, Randall's fiancée receiving chemo. They are playing Scrabble.] Randall: "Zarg" isn't a word. Randall's fiancée: But caaaancer. Randall: ...Ok, fine.
[Randall and Randall's fiancée (wearing a knit cap) are listening to a Cueball-like friend. A large thought bubble is above their heads and it obscures the friends talk. The text below, split in three is the only part there can be no doubt about:] Friend: So next year you should come visit us up in the mounta a and Randall and Randall's fiancée (thinking): "Next year"
[Randall and Randall's fiancée are getting married, with a heart above their heads. Randall's wife's hair is growing back.]
[Randall and Randall's wife (wearing a knit cap) stand on a beach, watching a whale jump out of water.] Fwoosh
[Randall's wife is sitting at a desk with her laptop standing on top of two books. Her hair has grown back a little more. Randall stands behind her.] Randall: Hey— Randall: you're doing science, Randall: and you're still alive. Randall's wife: Yeah!
[Randall and Randall's wife sit under a tall tree on a hill.] Randall: It's really only been two years? Randall's wife: They were big years.
[Randall and Randall's wife sit at a table in a fancy restaurant. Her hair has grown back even more. The waiter (Hairy) brings them a dish with a cover on it.] Waiter: Happy... Anniversary? Randall's wife: Biopsy-versary! Waiter: ...Eww.
While it is known that Randall's wife has since survived more than two years past the date of the invitation in Panel 6, it is unknown whether the invitation was later accepted. The followup comic Seven Years does not seem to include a visit "up in the mountains" among its various other recreational activities, but the one after it, Ten Years , does. However, since it is possible that the invitation was made up for the comic in order to represent the worry over any invitation envisioning the future at that time, it is possible that it was never proposed as depicted in the comic. Therefore, the real life invitation(s) which inspired the inclusion of Panel 6 in the comic could perhaps have referred in real life to an activity that is actually depicted in Seven Years or Ten Years , or to some other activity, which then may or may not have been realized.


Coverage

Explanation:
The caption "faraday cagematch" is a portmanteau of "faraday cage" and "cagematch".
A Faraday cage is a cage of conducting material that interferes and blocks out electromagnetic radiation like cell phone signals, provided the material is of the appropriate thickness and the gaps between the "bars" are significantly smaller than the wavelength of the radiation. A cage match is a type of professional wrestling match in which the participants fight in a ring enclosed by a metal cage. The comic caption is a play on the two terms, putting Cueball into a cage match in the Faraday cage that is blocking his reception.
Also the fact that Cueball gets hit in the face immediately after stating that the coverage is awful might be a joke about the different meanings of the word cover, boxing for example the word cover-up is a defensive technique, while phone coverage refers to the connection quality of his phone to the mobile phone network. The fact that Cueball, obviously referring to his phone signal, complains about awful coverage (caused by the faraday cage) while his head is also badly or not at all covered (caused by himself), which allows his opponent to strike him, might be described as ironically comedic.
The title text is a play on a rule in cage matches that states that a participant wins if they are first to escape the cage. Tunneling diodes are capable of fast operation, allowing a device to generate high frequency signals, which are more capable of penetrating the mesh openings in a Faraday cage.
Randall uses Faraday cages again in Faraday Tour .
[Cueball is looking at a phone.] Cueball: Man, the coverage here is awfu—
[Another man punches Cueball.] [Caption below the panel:] Faraday cagematch


Location

Explanation:
Ingress is an augmented reality location-based service game in which players have to visit certain real-world places marked by the game as containing in-game objectives called portals (much like in its far more well-known offspring Pokemon GO). The single guy in the comic owns a home surrounded by an abundance of portals, which makes it an attractive destination for the three friends who contact him via the computer. They are obviously not really friends of the guy, but just wish to come by because of the portals.
The portals in the comic are controlled by the green "Enlightened" team (and have links and a field), making them valuable resource caches for the "Enlightened" team, and priority targets for the blue "Resistance" team.
Foursquare , referenced in the title text, is another service that lets users check into places they visit for discounts in a similar way to how Ingress players visit portals for points. Unlike Foursquare places, which are businesses and public places such as parks, Ingress portals also include historic houses that are still private residences, as well as churches, so Ingress is more likely to reward people visiting a friend's house. "Space noises" refers to the ambient sounds when playing Ingress.
[Three people around a computer. One of them is typing.] Typing: Hey, party tonight? Typing: We'd all love to come see your new place! Reply (through monitor): Wait, what?
[Cut to guy sitting at a laptop.] Reply (through the guy's monitor): We want to hang out! Guy typing: We're not, like, good friends. Reply (through the guy's monitor): I know, but we were thinking about it and we really like you!
[Cut back to the three friends.] Typing: You should have us over tonight! Typing: For, like, an hour. Typing: It'll be fun! Reply (through monitor): Well, uh, sure.
[Cut to color-inverted image of the guy's house. Four Enlightened-controlled Ingress portals are in the guy's back yard.] Friends (off-screen): YESSSS! Guy (from inside his house): I still don't get why you're suddenly so excited to hang out.


Tags

Q: How do you annoy a web developer?

Explanation:
HTML is a markup language used in web development, and is the subject of this comic. The comic employs multiple poor HTML practices while asking the rhetorical question of how best to annoy web developers, effectively answering the question that it poses.
In HTML, all elements (except self-closing elements like  ) should consist of an open and close tag of the same type
Like this
 .
HTML (except in its formulation as an XML language—XHTML) has never been case-sensitive, but the practice of using uppercase tags for readability is long outmoded, and the mixing of cases in this example would definitely annoy a developer.
Another basic idea of HTML is that all elements should be properly nested. That is, any element whose open tag occurs inside a div must be closed before the div is closed.
NB: In practice, web browsers will error-correct nearly all these problems.
The rules of proper nesting also put restrictions on which tags can be placed where — "block" elements, such as
 cannot be placed inside "inline" elements, such as  , and inline elements must be placed inside a block element of some kind. Thus,
 is forbidden, even if the tags are closed in the proper order.
Further, web developers make a distinction between semantic and structural elements. Semantic elements contain a clue in their name as to what kind of an element they are — for example, an
 tag contains an article, such as a blog post or news article, while an
 tag contains an o rdered l ist. (It's wise to note that this is not an absolute rule; it's possible to put non-article content in an
 , it's just not recommended.) Semantic tags do not, however, indicate how their contents are to be displayed; your browser might display an
 in the default font, layout, and placement, while mine, a screen reader , might ignore everything on the page except
 s, and read
 s in a soothing voice .
Structural tags, on the other hand, give no clues as to what they contain; they just indicate how a web page is to be laid out.  and
 are structural tags; they can contain anything. Their definitions in HTML simply indicate that
 is a block tag (it can affect both what the text looks like and where it is on the page; by default, it is displayed in a separate block from the rest of the text in the page, and has at least one line break before and after its display) and  is an inline tag: it affects what its text looks like, but not where it is on the page. Without additional attributes, it's impossible for a browser to tell what's supposed to be inside a
 or a  , which means that my screen reader can't just pluck out the blog posts and read those.


Sky Color

Explanation:
The point of this comic is that often, curious children ask their parents simple questions about understanding how the world works.  Often, although the question is simple, the answer is not.  "Why is the sky blue?" is a common example, since most parents are not familiar with Rayleigh scattering , and thus are unable to answer the question.
Randall 's hobby is to make those questions even harder, so that the parents who are familiar with the subject (scientists, for example) will be stumped.
Another point of this comic is that we often think that we understand a scientific phenomenon (e.g. why is the sky blue?); however, a certain simple question (e.g. why isn't the sky violet?) can often uncover large gaps in our actual understanding.
Rayleigh scattering is the phenomenon that explains the color of the sky, where light of every wavelength gets scattered in the air by the inverse quartic (fourth power) of its wavelength as given in the comic. In the visible spectrum , blue light has a wavelength of 450–495 nm while violet has a shorter wavelength of 380–450 nm. Violet light does indeed get scattered more than blue light, however the lower portion of the spectrum for sunlight consists of blue light and eyes are much more sensitive to blue light than violet light. Furthermore, the sunlight contains more blue than violet to begin with as a result of the surface temperature of the sun. This leaves the impression of a blue sky. A good explanation, including why blue and not violet, can be found in Usenet Physics FAQ :: Why is the sky blue? , but note that human color perception is more complicated than described there.
The title text refers to a mirror image , and is discussed by the famous American theoretical physicist Richard Feynman in a famous BBC documentary [1] , as one of the problems which he used to have fun with first years (British English for first year student or freshman).
A mirror image is a virtual image produced by the reflection of light on a mirror. It's common to think of images in mirrors as being reversed left-to-right, as any text held in front of us will appear flipped. This is actually an issue of perception. In a plane mirror, images are reflected directly: the left side of your body will be reflected in the left side of the mirror, and vice-versa. The source of confusion is that people tend to think of a mirror image the way we would think of a person facing us.  When another person faces us, they turn around the vertical axis, placing their right hand on our left side, so seeing our left hand on our left side in a reflection seems like an inversion, even though it's a direct representation. By the same token, in order to hold text up to a mirror, we generally flip it around the vertical axis, so that the start of the text is on right, and the end on the left (in English, at least).  When the mirror reflects this, we see the text as backward, but the mirror hasn't reversed it, we reverse it when we turn it toward a mirror.
In other words, the vertical axis is only "special" because we're used to objects turning around it, so we come to expect that reversal, instead of a reflection.
You can induce a mirror to reverse left and right only --- by standing next to it instead of in front of it, facing along the plane of the mirror itself. If you lift your right arm, you can clearly see your image's left arm raising, without having to adjust for frame of reference. Similarly, you can induce a mirror to reverse top and bottom only by holding it flat above your head or laying it flat on the ground and standing on it (or perhaps standing under a suitably equipped bedroom ceiling). See this video for a demonstration.
[Science Girl and her mother, Megan, but with her hair up. Megan is at a desk and facing the girl.] Science Girl: Mommy, why is the sky blue? Megan: Rayleigh scattering! Short wavelengths get scattered way more (proportional to 1/ λ 4 ). Blue light dominates because it's so short. Science Girl: Oh. Science Girl: So why isn't the sky violet? Megan: Well, because, uh... ...hmm. [Caption Below the panel:] My hobby: Teaching tricky questions to the children of my scientist friends.


Honest

Explanation:
The phrase "let's be honest here—" is often used to soften a statement that might otherwise seem crass. Before Cueball can finish his sentence, he is interrupted by his friend, who takes the opportunity to honestly state his deepest feelings.
It is possible that Cueball's friend's last response, "Sorry," (which is on response to Cueball saying, "Too honest. Scale it back.") is insincere as a way of scaling his honesty back by not being honest in his next statement.
The human condition is essentially terrifying, having to try to keep up appearances all the time.
The title text could be a reference to angst , a word used in English to describe an intense feeling of panic — but the friend of Cueball proposes to work on a better understanding on his own fears.
Randall has mentioned having ADD, such as in 1106: ADD . People with neurological or psychological problems such as ADD often express having trouble with things in everyday life that other people seem to find easy.
[Two Cueballs are walking.] Cueball: I mean, let's be honest here- Friend: Ok.
[The friend is talking with his palm out.] Friend: I don't understand why anything happens and I'm confused and scared and trying really hard all the time.
[The two Cueballs look at each other.] Cueball: ...Too honest. Cueball: Scale it back. Friend: Sorry.


Evolving

Explanation:
In a Pokémon game, a player goes out in search for the eponymous creatures. Many Pokémon can be found directly in the wild, but there are also a lot of Pokémon that require training and growth, to cause them to "evolve" into new Pokémon. "Evolve," the game's term, is a misnomer which earned itself quite some controversy in the past; in reality, Pokémon "evolution" is more akin to puberty or metamorphosis, since instead of the entire species of Pokémon acquiring changes through an extended period of time, one specific member of the species grows instantly to the "higher stage." At that point in the game, the Pokémon glows before transforming into the new form, then stops glowing, and the very same text "What? XXX is evolving!" is used (see this video or those screenshots for instance). The changes of such a transformation can be quite dramatic ... or not.
This comic depicts the "evolution" of bacteria as observed by a Biologist in the same format as the game Pokémon. Here we have Staphylococcus aureus , which is not a desirable bacterium (it causes Staph infections ) which evolves into "Methicillin-resistant Staphylococcus aureus " . Methicillin is an antibiotic. If the bacterium becomes resistant, it means the antibiotic will be less effective against it, making infections harder to treat. Thus the observer is not pleased with such an evolution.
The title text references this by suggesting that biologists do not want bacteria to evolve in this way, as opposed to Pokémon where you put a Pokémon on the "front lines" as much as possible to gain it experience and hope it evolves. A point of irony is that Pokémon evolution can easily be prevented, by using an Everstone, or stopped, by pressing the B button in the game controller during evolution, especially if there are Pokémon that one does not want to evolve. The bit about the front lines is that, if a bacteria colony is exposed sufficiently to an antibiotic, those bacteria with any level of resistance to the antibiotic are less likely to be killed by the antibiotic, and are able to reproduce in spite of the antibiotic. Most future generations of bacteria now have this level of resistance instead of just a small subset. This makes the likelihood of future more resistant and harder to treat mutations even more likely.
Staphylococcus aureus is a very common bacterium, that under an electron microscope looks like the xkcd drawing, and is the major cause of staph infections in the nostrils and skin. Hospitals are often plagued with outbreaks of Methicillin-resistant Staphylococcus aureus (MRSA), which is very difficult to treat as the typical antibiotics do not work on it.
[Bacterial cell culture.] What? Staphylococcus aureus is evolving!
...
Off-screen: Aww, crap. Staphylococcus aureus evolved into Methicillin-resistant Staphylococcus aureus!


Nothing to Offer

Explanation:
"I have nothing to offer but blood, toil, tears, and sweat " is a famous phrase in a speech given by Winston Churchill , which would be heard on the radio in the 1940s. The comic then goes on to list numerous other increasingly obscure bodily fluids , including through the title text, ending humorously with gin (which Churchill was partial to).
The fluids in order: blood , tears , sweat , spit , bile , vomit , urine , mucus , semen , earwax , lymph , gastric acid , sebum , pus , endolymph , intracellular fluid , blood plasma , vitreous humor , feces , pleural cavity fluid , chyle , synovial fluid , peritoneal fluid , cerebrospinal fluid , pericardial fluid , sputum , aqueous humor , perilymph , chyme , hydatid fluid , interstitial fluid , and rheum . The partially obscured ones near the end are taken by process of elimination. CHLY- seems to be a typo for CHYL(E).
[Replace 'gin' with 'tea' for all other Bri'ish people]
[Radio on a dresser.] Radio: I have nothing to offer Radio: But
Radio: Blood, toil, tears, sweat,
Radio: spit, bile, vomit, urine,
[Text is now bleeding through the background and gets obscured then cut off.] Radio: mucus, semen, earwax, lymph, gastric acid, sebum, pus, endolymph, intracellular fluid, blood plasma, vitreous humor, feces, pleural cavity fluid, chlye, synovial fluid, peritoneal fluid,


Broomstick

Explanation:
Megan plays the part of Dorothy , the protagonist of The Wonderful Wizard of Oz . Dorothy has been trapped in the Land of Oz due to extreme weather and must obtain transportation home. An off-screen character, presumably the Wizard of Oz himself, offers her a ride if she obtains the The Wicked Witch of the West 's magic broom. Megan wears Ruby Slippers and uses them as a bargaining chip to obtain the Witch's broom.
The "little dog" offered in the title text is Dorothy's faithful companion Toto .
The Wicked Witch of the West is a fictional character and the most significant antagonist in The Wizard of Oz , which is based on L. Frank Baum's children's book The Wonderful Wizard of Oz . In the 1939 version of The Wizard of Oz , the Wicked Witch flies on her broom over the Emerald City demanding Dorothy's surrender, and the Wizard demands the destruction of the Witch with her broom as proof, in exchange for granting the wishes of Dorothy and her companions.
The point of the comic is to show how easily Dorothy could resolve the situation if she was willing to forsake both her traveling companions and her pet. She leaves Toto with the Witch; it is unclear whether she plans to retain possession of the broom and return it in order to collect him, or plans to abandon Toto as well. She will also leave Oz completely at the mercy of said witch by giving her the Ruby Slippers and leaving with the Wizard.
It should be noted that this resolution defies the canon established in the movie, as nobody could remove the slippers as long as Dorothy lived , presumably including Dorothy herself. Additionally, it turns out that the Wizard was a fraud and was unable to take her home, and ironically it is the ruby slippers that did so.
The Wizard of Oz was also referenced in Five-Minute Comics: Part 4 , and iOS Keyboard .
[Megan wearing red shoes talking to somebody off-screen.] Off-screen: Bring me the broomstick of the Wicked Witch of the West and I'll take you home. Megan: Got it.
[Megan wearing red shoes standing before steps.] Megan: You can have the slippers if you let me borrow your broom. Off-screen: Deal.
[Megan carrying a broom and singing without wearing the red shoes.]
[Megan flying in a balloon over three Wizard of Oz characters.] Megan: That was easy.


Instagram

Explanation:
As indicated by the title, this comic is an allegory for a controversy over Instagram , a photo-sharing social network now owned by Facebook . In December 2012, Instagram changed their terms of use , allowing the network to sell user-uploaded images, without profit to the content generators. This infuriated many users, who closed their accounts or stopped uploading images.
In the comic Cueball tells his Cueball-like friend about his problem with Chad, who just sent him a note telling him that he no longer wants to store all this stuff that Cueball has left in his garage. Cueball left it there because Chad has nice shelves and lets him in to see his stuff whenever he wishes, so that was really convenient.
Chad's note tells Cueball that he has a month to move his shit — after that he will try to get rid of it by selling it on Craigslist . This is a website where individuals can contact others interested in buying or selling goods. As a verb, it means to sell something on Craigslist. ( FYI is an abbreviation of For Your Information ).
Cueball is outraged, as this is not way to run a storage business . But when his friend asks him if he paid anything for this "storage business", it turns out that he did not. The friend then concludes that it is not a storage business.
This is exactly the problem with Instagram (or its users). A user does not pay anything, but to create an account you have to sign a terms of service/end user license agreement. A user has thus effectively signed their consent to whatever Instagram has written. Instagram can then change these terms if they give a forewarning (as Chad has done here). However, most users don't read the terms before clicking the "I agree" option, so it can come as a shock when Instagram uses the data in a way the user hadn't anticipated.
Instead of getting angry Cueball should thus just go and remove his stuff, but instead he is just going to almost (but not quite) stop giving Chad any more stuff.
This is also making fun of those Instagram users that complain about the new way of using their data, but at the same time keep uploading more pictures. The users have often developed a kind of addiction, so they cannot just stop sharing their life (in pictures).
In the title text Cueball continues with an idea of calling the cops. He thinks that Chad is a thief. He thus ignores that he left the stuff at Chad's house of his own accord. And after Chad has been arrested (which will of course never happen) he wishes to move all his stuff to another house, just to continue to get free storage.
There are two major flaws in this logic - and it is the same with the logic of the disgruntled Instagram users. You cannot accuse Instagram of stealing because it was you who gave them the images in the first place, and it is irresponsible to assume that this will not happen if you give your photos to another free social networking service (e.g. Facebook ).
These kind of issues (with Facebook as the evildoer) are also the subject of 743: Infrastructures and 1390: Research Ethics .
[Cueball, raising a hand, is talking to his Cueball-like friend who is sitting by his computer.] Cueball: I've been putting all my stuff in Chad's garage. Cueball: He has nice shelves. Cueball: And he lets me in to see it whenever I want.
[In the next panel, without a frame, there is a close up of a note. Above the note is a small black frame with Cueballs comment:] Cueball (off-panel): But I got this note from him: [The note:] Dude In like a month im gonna Craigslist all that shit you left in my garage Just FYI -Chad
[Zoom in on Cueball who lifts both hands palms up.] Cueball: It's an outrage! This is no way to run a storage business! Friend (off-panel): Are you paying him to look after your stuff?
[Final frame almost like the first frame, but Cueball has taken his hands down.] Cueball: No. Friend: Then what he runs isn't a storage business. Cueball: Well, I'm this close to not giving him any more stuff. Friend: That'll teach him.


Tests

Explanation:
The first present Megan opened contained a home biology lab kit, including the equipment needed to perform a Gram stain. Gram staining is a technique used in microbiology to separate bacteria into two broad categories based on the structure of their cell walls. The sample is treated with two different dyes: first a purple dye, then secondly a pink one. When subsequently examined under a microscope, "Gram-positive" bacteria retain the purple color of the first dye, whereas "Gram-negative" bacteria do not, allowing the second pink stain to show. All Megan's presents have been stained pink, and are presumably therefore Gram-negative.
In the process, she has damaged the other presents, hence Cueball's wish that she had opened another present first.
The title text refers to two bacteria commonly used as controls to confirm that the technique has been correctly performed: Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative). Neither are bacteria you want to be coming into contact with in any substantial quantities [ citation needed ] , hence the need to stop accepting presents from " That Guy ".
[Megan pouring a bucket of purple liquid on the presents at the base of a Christmas tree.]
[Megan pouring a bucket of pink liquid on the presents at the base of a Christmas tree.]
[Megan looking at the soaked presents.]
Megan: All my presents appear to be Gram-negative. Cueball: I wish you hadn't opened the home bio lab kit first.


Communion

Explanation:
This comic plays on the Christian doctrine that the Holy Communion bread and wine are Jesus' flesh and blood. It is based on the words of Jesus from the synoptic gospels and Paul's first epistle to the Corinthians during the Last Supper , today used by the priest as Words of Institution . According to the Roman Catholic doctrine of transubstantiation , as well as in the Eastern Christian tradition, the substance (using the Aristotelian concept that all things have an accident, or physical make-up, as well as a substance, or true nature/purpose) of the bread and wine change to Jesus' flesh and blood, while their accidents remains the same. Many people, including many Catholics, believe this concept means the bread and wine literally turn (i.e., their accidents changes) into Jesus' flesh and blood during the ceremony. Some Protestant denominations reject this doctrine, both its actual and misunderstood application, with some taking the words as wholly symbolic of Jesus' sacrificial death and others believing the bread and wine create a real spiritual connection to Christ but do not change their substance.
In the second panel, Danish accurately describes what would happen at a traditional Christian Christmas service, though in such a way as to make it sound macabre.
After walking and thinking in panel three, she makes it more macabre when worrying that they, again, may have gotten hold of the wrong child for the sacrifice needed to drink blood and eat flesh.
The title text further spoofs the common understanding of the doctrine of transubstantiation and elaborates on Danish 's concern in the last panel by supposing that the act of taking a sip of wine during Holy Communion turns that wine into the blood, not of Jesus, but of a decades-old murder victim.  Alternatively, the title text could be interpreted as saying that the wine actually acquires Jesus' DNA, and that Jesus was "killed" in the 1970s.  The police, who investigated Jesus' 1970s death, would then have his DNA on file.
It should be noted that saliva includes DNA, so the positive result may be the DNA from the person who spit the wine/blood out and does not necessarily mean that that person was murdered by the church in order to prepare the wine/blood. This could be a reference to the resurrection of Jesus.
[Cueball and Danish are taking a stroll.] Cueball: How was Christmas? Did you go to church?
Danish: Yup. We celebrated the birth of a child, then we ate of his flesh and blood.
[Silence from Cueball.]
Danish: Seriously hope we got the right child this time.


Proof

Explanation:
Zeno of Elea was an ancient Greek philosopher who devised several apparent paradoxes of motion called Zeno's paradoxes . Here are the two relevant to the comic:
Arrow paradox: At any instant in time, an arrow suspended in mid-air is no different from an arrow in motion. How, then, can motion occur? (Answer: calculus [all objects have a velocity].) The lawyer presumably intends to use this argument to prove that his client could not have used the arrow to commit murder. Another possibility was that it is impossible to hit a person in motion.
Dichotomy paradox: Suppose I need to go from point A to point B. First I must walk halfway there: half of the distance between A and B. Then I must walk half the remaining distance, which would bring me to three-quarters of the original distance; then I must again walk half the now-remaining distance to reach a point seven-eighths of the way from point A, and so on. Because I would have to take an infinite number of non-zero steps, I will never reach point B. By the same argument, the lawyer in the comic can get closer and closer to the judge's table, but never reach it.
There are two possible law vs math/logic puns in the comic, on the words "approach" and "proof." " Approach the bench " is a legal term meaning to have a private conversation with the judge; approach in calculus means an infinite process where a function value gets closer and closer to a limit value that it never actually reaches, reminiscent of Zeno's paradoxes. "Proof" is also ambiguous, with a different meaning in formal mathematics than in jurisprudence . See Proof (truth) and Mathematical Proof , for example.
Gottfried Leibniz is the co-inventor of calculus (along with Isaac Newton; see 626: Newton and Leibniz ). If Leibniz were to testify in this imaginary trial, he might argue that calculus invalidates Zeno's paradoxes, because the moving arrow has a different velocity than a stationary one (the function describing the motion has a nonzero derivative at the point), and the infinite series in the dichotomy paradox has a finite sum. Both Zeno and calculus assume a continuous, infinitely divisible, ideal spacetime (as does quantum mechanics ); a different solution would be available if spacetime turns out to be discrete. However, Zeno is arguably not concerned with actually calculating the correct answer. In the real world, Zeno can be trivially disproven simply by moving and reaching a desired target (it is said that Diogenes the Cynic reacted to the paradox by wordlessly walking to a destination, to demonstrate his contempt for it). It remains a question of debate whether a mathematical approach addresses the central points in Zeno's arguments.
994: Advent Calendar is also about Zeno.
Zeno: My client couldn't have killed anyone with this arrow, and I can prove it! Judge: I'd like to examine your proof, Zeno. You may approach the bench. Zeno: —But never reach it!


Resolution

Explanation:
This New Year comic is a little reminder that it's the last day of 2012 , and it's time to make your New Year's resolutions !
Cueball wants to break a very common habit of resolving to do something (go on a diet, for example), not doing it, and then trying the same, dysfunctional plan again, thinking it will work "this year." This is another way of stating a common folk definition of insanity: to keep doing what you always do yet expecting different results.
The irony is that Cueball resolved the same thing last year, and it is implied it didn't work, but he says it'll be different "this year."
The title text is a parody of the saying "if at first you don't succeed: try, try, try again."
Cueball: I'm scared of being stuck—thinking I'm fixing things about myself but never actually changing. Cueball: My 2013 resolution is to break out of loops. To recognize when I'm not making progress, stop yelling at myself, and try a different approach. Out of panel: Wasn't that also your resolution last year? Cueball: Yeah, but this year's gonna be different.


Kolmogorov Directions

Explanation:
Andrey Kolmogorov was a mathematician who worked, among other things, on defining computational complexity. Roughly speaking, the Kolmogorov complexity of a string (of bits, words, symbols, etc.) is the shortest description that allows an accurate reconstruction — or, in some variants, the length of the smallest program which will output the original string.
Cueball 's method of giving directions is very reminiscent of Kolmogorov's method of determining complexity. However, it is unlikely they know all the presidents, nor can calculate prime numbers in their heads, and so will have trouble with certain parts. These directions may have minimal Kolmogorov complexity, but they are non-intuitive and are likely not the shortest or quickest way to get there, considering that they consist mostly of left turns.
This is not the first time Cueball has had difficulties with directions, and here we see he hates giving directions as much as he hates receiving them.
The joke in the title text is that Cueball just sent his friend to a store to buy a GPS device to give him the correct directions. (By the time this comic was published, GPS-enabled smartphones had already largely displaced dedicated GPS devices, [1] but Cueball could be talking to a person who does not wish to own a smartphone.)
[Cueball on the phone.] Phone: How do I get to your place from Lexington? Cueball: Hmm... Cueball: Ok, starting from your driveway, take every left turn that doesn't put you on a prime-numbered highway or street named for a president.
[Caption below the panel:] When people ask for step-by-step directions, I worry that there will be too many steps to remember, so I try to put them in minimal form.


Conditioning

Explanation:
Herein, the author devises a method of addressing the issue of drivers who turn up their music to irritating levels which usually results in a lot of bass coming from the car — the low frequencies being the ones that most easily penetrate the car and travel farther, thus being more audible to those around the car.
As the title suggests, the idea is to condition animals to respond to a thumping bass. The machine is described as working as follows: every few hours, the bass would turn on, and the box would dispense food behind an opening designed to look like an open car window. Over time, local wildlife would flock to the box to get the food from inside, and would become trained that the sound of a subwoofer means that they can get food by flying through a car window.. Eventually, the animals would respond to any low music, including that played by cars.
The end result would be that the local wildlife would approach, and presumably attempt to enter, any car that has that same thumping bass. Drivers, in turn, would cease to turn up their music in order to prevent the groups of animals from chasing after their cars, thus solving the problem of annoyingly loud bass. This behavior modification can itself be seen as a somewhat different form of conditioning .
Although this plan may seem far-fetched, a similar scheme was seriously proposed in the United Kingdom during World War I to condition seagulls to associate a submarine's periscope with food, which would give away the locations of enemy submarines as the gulls flocked to their periscopes being raised.
The title text is a dialogue about using a similar method of conditioning to send animals after a visiting Pope . Why someone would want that to happen is left to the reader's imagination, although papal visitations usually disrupt the local communities with onerous traffic and special and ostentatious ceremonies, and do attract huge crowds of dignitaries, celebrities, the faithful, the curious, and attending purveyors of foodstuffs and trinkets. Not to mention the impact to the local AirBnB market. Or it could just be Black Hat, who would not need any particular reason for this sort of behavior, and might choose the Pope because of his highly recognizable outfit.
Every few hours, subwoofer plays throbbing bass for 10 seconds... [With arrow pointing to subwoofer.] ...then bread crumbs are dispensed into box [With arrow pointing to bread feeder machine.] Opening [With arrow pointing to feeder opening shaped like a driver side car window.] Local wildlife [With arrows pointing to birds and a squirrel.] Protip: Leave this device in your yard for a week, then watch as the problem of loud music from passing cars solves itself.


Sick Day

Explanation:
This pie chart for the most part reflects the usual experience of being sick — tossing and turning in bed and cleaning up mucus and other bodily fluids from facial orifices— in addition to a few ponderings of a rather more scientific bent.
The "army of critters that patrol my body" would appear to refer to the human immune system , which is made up of various cells and processes that actively fight infections and pathogens.
The punchline appears to be "pondering hooking an aquarium pump to my sinuses," which indicates that Randall 's sinuses were completely clogged with mucus, which made him wonder whether hooking up an aquarium pump would help clear them out, perhaps akin to a Neti pot . Studies on nasal irrigation, however, have had mixed results, and the practice may not in fact be beneficial.
Randall's Wikipedia path: Virus → Immune system → Innate immune system → Parasites → List of parasites of humans → Naegleria fowleri → Primary amoebic meningoencephalitis .
Naegleria fowleri is known as the brain-eating amoeba. It is found in warm bodies of stagnant fresh water and causes the disease primary amoebic meningoencephalitis, a rare but highly lethal condition. Although N. fowleri are not commonly found in aquariums, Randall's Wikipedia wanderings force him to conclude that attempting to clear out his sinuses with an aquarium pump is too risky. Since this danger would presumably not be present at all with an unused, sterilized aquarium pump, the comic may be referring to a particular pump currently in use and close at hand.
[This comic shows a pie chart with 5 slices, each with a label and a line pointing to these five different sized slices. There is a caption above the chart:] Activities while sick: [The labels on each slice is given in clockwise order starting from the top. The percentages are estimated from the image and are noted in the square brackets before the transcript:] [54%] - Shifting around in bed feeling my skin crawl [24%] - Wiping various face holes [5%] - Staring at a news site but not reading it [14%] - Thinking about how cool it is that I'm partly made of an army of critters that patrol my body ruthlessly dispatching anything they find trying to prey on me. [3%] - Pondering hooking an aquarium pump up to my sinuses


Rubber Sheet

Explanation:
This comic refers to a common analogy used to explain how mass distorts space-time — a bowling ball resting on a sheet of rubber distorts the sheet due to its weight. The system has some qualitative features in common with gravity; it's often misused to show that "mass warps spacetime" ( 895: Teaching Physics ).
The next part of the original analogy explains a black hole: the slope of the sheet becomes so deep that you can't climb out from the bottom any more, similar to a black hole, which even light can't escape from. However, the comic subverts the analogy, and the sheet becomes a trampoline instead.
Reading onwards, it seems that Beret Guy is just messing about with the scenario.
The line "Imagining is fun! " is also a homage to Richard P. Feynman 's "Fun to Imagine" Series of Interviews. The power of Beret Guy's imagination—so that he can physically experience what he imagines—is reminiscent of 248 .
The title text also states that the rubber sheet, broken rope and trampoline are still all about physics (see also 435: Purity ).
[Beret guy is standing on a giant bowling ball on a rubber sheet. Megan is watching.] Beret Guy: Imagine a giant bowling ball on a rubber sheet. Beret Guy: The ball's weight makes a dent in the sheet.
[A rope is pulling the ball down into the sheet.] Beret Guy: Now imagine a rope that pulls the ball down even further. Beret Guy: ...Annnnd...
[Rope lets go. Ball is catapulted with Beret Guy on it.] BOOOIING Beret Guy: Wheee
[Beret guy and ball are falling back down.] Megan: ...Oh. I thought this was about physics. Beret Guy: Imagining is fun!


Countdown

Explanation:
The comic shows a seven segment display (aka calculator-style numbers ) with a countdown. Black Hat explains that it is a countdown, maybe to a supervolcano eruption. However, an unfortunately placed picture blocks view of the full display. Due to the form of a seven-segment display, the first digit could be 0, 6, or 8, and five digits are completely blocked by the picture. Cueball is worried and asks him to move the picture, but Black Hat lazily or teasingly refuses to move it.
He has already teased that he doesn't know what the countdown is for. His reply can either be understood as if he does not know which one of the ( seven potential ) supervolcanos it is counting down to, or to which other cataclysmic event it is a countdown for (such as a meteor strike or global nuclear war for instance - it could also just be a general Doomsday Clock ). Since it seems to be Black Hat's countdown, it is safe to assume that he knows both what it counts down to and when it stops, but he just likes to mess with peoples' minds.
The fully visible part starts at 2409, and based on the pace of the scene, it seems to be in seconds. Thus, it is unclear when the eruption might occur. If the obscured digits are all 0s, it could be as soon as 40 minutes. On the other hand, if the obscured digits are '899 999', there's another 2.85 million years to go; if they are '000 001', we have a little more than 3 years.
The choice of the picture is probably also interesting. The image is distorted enough that you can imagine it as being two very different images.
In either case, it could make sense. If it is a volcano, the supervolcano clock makes sense. On the other hand, we are talking about the possible end of the world as we know it, so the sun setting upon humanity could be a great metaphor.
The title text: "For all we know, the odds are in our favor" could imply the assumption that since we can't see the digits behind the picture, we can treat them as random. If so, chances are only 1 in 300 000 they are all zeros. However, because of statistical principles such as Benford's law , the digits are not entirely random, and the odds are higher than 1/299 999 for all the digits to be zero since the middle 4 digits are zero.
In an alternative view, the strip is not about pondering at distributions of digits on an oracle countdown. It's more of a grim view of our natural disaster prediction capabilities. As they say – the question is not if it will happen but when it will happen. "Move the picture" would mean investing in research and warning systems - that would correspond to shifting the picture to the left. If we disregard the 40 minutes, but instead think of it as an arbitrary interval of interests, minuscule as we folks have them, say - one's lifetime; or grimmer yet - some term of office . Because, hey, year after year passes and no apocalypse has been observed - the empirical odds are low indeed. An interesting question is what we would use the knowledge of the timing of our impending doom, if it is an event we can do nothing about, such as stopping a supervolcanic eruption or a large asteroid with a direct impact course on Earth. Would we not have lives more happily for our remaining years, how few that might be, while not knowing... On the other hand, if the event is something we might prevent given enough time to plan (and the funding resources such knowledge would ensure), then it may have saved us if we moved the picture just in time!
Using a countdown theme for comic #1159 could be a subtle joke, as 11:59/23:59 is one minute to midnight (on the Doomsday clock!).
Supervolcanos were also referenced in the title text of 1053: Ten Thousand and it is the subject of in 1611: Baking Soda and Vinegar .
[Black Hat is sitting with his laptop on a desk when Cueball, standing behind him, looks up on the wall and asks him about the large digital countdown timer with red numbers which is hanging high up on the wall. It has a white frame around the black display with the red numbers. Most of the left part of the counter is covered by a framed picture that hangs on a string attached to a nail above the counter. The picture depicts either a setting sun reflecting in an ocean or an exploding volcano with lava flowing away from it. The picture does not block the left-most part of the frame around the counter, and it is also possible to see the two left-most lines of the first digit on the countdown, so they are both turned on. This proves that the numbers go all the way to the left end. The next five digits are covered by the picture. Then one digit is only partly covered, as only the two most left lines are not visible. From the visible lines, it is though clear that this digit shows a 0. The next seven digits are fully visible, giving eight discernible digits.] 00002409 Cueball: What's that? Black Hat: Countdown. [Same picture, but Cueball is looking at Black Hat. The counter counts down.] 00002400 Cueball: To what? Black Hat: Supervolcano, I think. I forget which one. [Cueball looks up again for about 18s (between 2nd and fourth image) - beat panel.] 00002396 [Cueball looks at Black Hat again.] 00002382 Cueball: Maybe we should move that picture? Black Hat: Too hard to reach. It's probably fine.


Drop Those Pounds

Explanation:
The comic presents a flyer with text typical of a ubiquitous advertisement for a "Weight Loss Program". However, the image at the bottom of the flyer and the text below the flyer make it clear that the flyer is actually an advertisement for a trebuchet club. This unexpected meaning is meant to highlight the ambiguity of the flyer's content. A counterweight trebuchet is typically a gravity powered siege engine, which was originally used to attack fortifications. It works by dropping a raised counter weight to rotate a throwing arm, launching a projectile on a ballistic path. The phrase "We'll help you hit your target by dropping 30 pounds FAST" is where the ambiguity is produced. In the context of a weight loss ad, the "target" would be a rhetorical device referring to the weight which one wishes to achieve. In the context of a trebuchet club, the target is a literal location which one is trying to hit with a projectile. Likewise, a weight loss ad may indicate that a client could quickly lose 30 pounds (~13.6 kg). However, in this context, the 30 pounds being dropped is either the counter-weight - which is dropped to provide a trebuchet with its power, implying a rather small trebuchet - or the projectile itself being dropped at the target - it will be slower than the counter-weight but definitely still much faster than any weight loss program.
The only hint that the flyer advertises a trebuchet club is in the drawing at the bottom of the flyer, which appears to show two individuals pondering a ballistic path towards a castle tower, though no trebuchet is shown.
The text below indicates that this flyer "may have been too subtle". The title text suggests that, if the flyer is indeed too subtle a form of advertisement, they will use the LEAST subtle options of announcing their club's existence — likely by using their trebuchet to attack the town.That would certainly get the club some attention!
See also 382: Trebuchet .
[We see a poster taped to a wall. It has Megan and Cueball in the bottom left, a silhouetted crenelated tower in the bottom right, and a thin arc between them. It reads:] Struggling with those 2013 resolutions? We'll help you hit your target By dropping thirty pounds fast [Small print.] WEB: http://[illegible].com CALL: [illegible]
The flyer for our trebuchet–building club may have been too subtle.


Hand Sanitizer

Explanation:
The number of germs that would be left after using the hand sanitizer is 200 million times 0.01%. 0.01% is equivalent to 0.0001 in decimal, so the multiplication is 200 000 000 × 0.0001. That is 20 thousand germs, which is still a surprisingly large number of germs. Recently, scientists have shown that it only takes 20 virus particles to infect someone (with analyzed virus; not all germs are equally effective). However, they have also previously noted that the effectiveness of hand sanitizer is actually higher than 99.99%, but it's a bit awkward to print a more precise decimal in an advertising slogan. (Several brands actually kill near 100%, but don't want to risk going to court for false advertising because a few germs got past.)
"Hipster CDC" is a combination of the acronym for the Centers for Disease Control and Prevention , an organization dedicated to studying infectious diseases and limiting their spread, with the label hipster . Hipsters form a cultural group associated with a distaste for popular culture; they stereotypically talk about how bands, authors, etc. were better before they "went mainstream" and proclaim that they liked a certain thing "before it was cool."
The title text extends this sensibility to the flu, which in fact did peak years ago, such as in 1918, when a world-wide flu epidemic killed tens of millions. The humor lies in the notion that the "Hipster CDC" apparently approves of the time when the flu was more widespread and fatal, while most people consider the diminishment of the flu is a good thing. This could be a jab at hipsters' common insistence on liking things before they "go mainstream": many things, before they go mainstream, just aren't very good, and therefore hipsters' taste in things is highly questionable.
[Cueball looks at a poster while holding a bottle.] Poster: An invisible sneeze droplet can contain 200 million germs!
[Same scene, except Cueball is looking at the bottle.] Product label: Our hand sanitizer kills 99.99% of germs!
[Cueball types on a calculator while still holding the product.] Cueball (typing on calculator): 200 000 000 × 0.01% =
[Cueball holds down his calculator.] Cueball: Ew.


Log Scale

Explanation:
This comic strip is a tip , specifically the first science tip .  As with most of Randall's tips, it is technically interesting for some applications but not very practical.
Uranium is stated to have 76 million MJ/kg, while the next highest material shown on the graph (gasoline) has 46 MJ/kg. Thus the uranium graph should be taller by a factor of 76,000,000/46 = 1.652 million. So, if the gasoline graph were 9mm in height, the uranium graph should be a bit more than 14.868 million mm tall, or nearly 15 km (9.2 miles) tall. Thus the need to fold the paper.
It should be noted that the method of extracting energy from the first 4 materials ( combustion ) is completely different from the method used with uranium ( nuclear fission ). If the technology existed to use nuclear fusion , then the first 4 materials would yield a higher energy density than uranium.
A log scale is a way of showing largely unequal data sizes in a comprehensible way, using an exponential function between each notch on the y axis of a graph. So for example the first on a Y axis of a graph using a log-10-scale would be 1, then 10, then 100 and 1000 for the fourth. A log/logarithmic function is the inverse of a corresponding exponential function . A log-scale version of the chart in the comic would look like this:

The log scale can also be abused to make data look more uniform than it really is. On a log scale the energy density of uranium looks larger than that of the other materials, but not dramatically so. The joke is that if one wanted to make their point "properly," they would go ahead and use ridiculous amounts of paper to show the difference between bars using a linear scale; this method would focus more on the shock factor of the differences in question, and less on actual communication/representation of data. Cueball seems to be passionate about the MJ/kg of uranium, so he would rather demonstrate the grandeur of the data than use a more efficient scale.
See these examples for well known day-to-day measurements which are measured on a log-scale.
The title text mentions computer scientist Donald Knuth ; the fictional notation is a parody of Knuth's up-arrow notation . Using paper thickness as the basis for a log scale would probably give the exponential function a very large base. However, it can be noted that Knuth's up-arrow notation can handle numbers far, far larger than this paper stack notation; for example the number 3↑↑↑3, also known as Tritri [1] , very compact in up-arrow notation, would require a number of iterations pinned to the stack on the order of several trillion. 3↑↑↑↑3 , also known as Grahal [2] , would require a number of iterations that is not only too large to write down, but attempting to write that number using the same paper stack notation would require printing off a second stack of several trillion iterations just to hold the number pinned to the first stack. By repeating this multi-stack repetition, you reach the limit of up-arrow notation.
It should be noted that Randall has used log scales in past comics.
[A bar chart on a piece of paper, with a second piece of paper attached to it.] [Title of the bar chart] fuel energy density of different materials in megajoules/kg [Values of the first 4 bars on the paper] 19 24 39 46 [The different bars for Sugar, Coal Fat and Gasoline and Uranium on a linear scale with the bar for Uranium exceeding on the attached stack of paper] [Labels of the 5 bars on the paper] Sugar Coal Fat Gasoline Uranium [The uranium bar on the chart goes off the page onto a huge strip of paper folded up into a stack slightly taller than Cueball.] [Value on the top end of the paper strip] 76 000 000 [Caption below the panel:] Science Tip: Log scales are for quitters who can't find enough paper to make their point properly .
This comic was seen in the What If? book, taken from "a certain webcomic".


Debugger

Explanation:
Cueball mentions to Megan that he can't understand how his mind works, the same mind he uses to understand how things work, and he's not sure if this is a problem. In other words, if he can't understand how his mind works, then how can he tell that it does in fact work and that his perception of reality is accurate? Ordinarily he would use his mind to figure it out, but if his mind really doesn't work, then he'll probably never determine that his mind doesn't work. Not only that, he can't even trust his brain to tell him if his inability to understand his own brain is an issue. Understandably, he's a little unsure of how he should feel about this.
Per the comic title, a debugger is a piece of software used by programmers to find bugs in the applications they are making. The title is an allusion to that debuggers are very much like our brains in the aspect described above - most programmers don't understand how debuggers internally work, and they can't be sure that debugger is bug-free - if there is a bug in the debugger itself, it can't be accurately used to find bugs.
The title text alludes to the above problem, in that if a website's "report a bug" page is buggy to a degree that it prevents the actual reporting of a bug, then users cannot use the form to report that the form itself is broken. Thus it can take quite some time before the site administrators realize this error, if they do at all, as unless they test it themselves, the administrators are likely relying on users to report problems they find, which they can't, making it appear as if there are no problems. This is somewhat analogous to the "brain" dilemma in the main comic, where the usual problem-pondering and resolving method itself can have a problem, but there is no straightforward way to tell.
[Megan and Cueball are at the top of a grassy hill, rendered in silhouette. Megan is lying down on the grass while Cueball is sitting.] Cueball: I don't understand how my brain works.
[A close-up of the two characters. Megan lifts her head slightly.] Cueball: But my brain is what I rely on to understand how things work.
[The shot zooms out again.] Megan: Is that a problem? Cueball: I'm not sure how to tell.


Home Alone

Explanation:
Home Alone is a popular 1990 film in which the child protagonist Kevin McCallister (portrayed by Macaulay Culkin ) is accidentally left alone in his house when his family goes on vacation, and has to thwart a burglary all by himself. In the movie, McCallister comes up with a variety of ingenious traps and schemes (usually involving jury-rigged toys and household items) to harass, injure and eventually incapacitate the burglars, which was the film's defining feature. On a more general level, the films revolve around the classical trope with an underdog defeating a much stronger opponent (the burglars), through his own ingenuity. The film spawned a series of sequels (4 as of 2012, the first of which also starred Culkin) all with a similar premise to the original.
This strip, however, proposes a reboot of the franchise, with the main change to the film being that of an age-reversal, so the story is now about an adult man setting needlessly harmful traps to hurt defenseless children breaking into his house. This would likely be seen as distasteful at the very least, and would probably lead to a negative reputation for the film. The title text adds another punchline when it is revealed that the reboot also stars Macaulay Culkin in the same role. This may suggest that the age-reversal gimmick was done to allow for him to star in the film as the same character despite growing up since the beginning of the franchise. This would be a rather misguided attempt to revive his career, and would probably just prevent any further success.
The scene depicted in the strip is an adaptation of an iconic scene from the first movie (used heavily in advertising) where McCallister hangs two paint cans in strings above the staircase, and let them swing down to hit the burglars in the face.
[Aged man standing at the head of a flight of stairs. A paint can on a rope is swinging into a child at the foot of the stairs. A child on the floor is in a semi-fetal position and crying.] Child: Ow!! Child on floor: Waaaaaaaaa! Rejected movie ideas: Age-reversed Home Alone reboot.


Amazon

Explanation:
The Amazon River in South America is the second longest river in the world and by far the largest by waterflow. Amazon.com is a website that specializes in commerce and selling goods over the internet. The "round 14" suggest they are being compared in different criteria in a sort of competition. With such different systems, we can assume that most of those comparisons were similarly funny. The title text mentions two other criteria of comparison.
The measure of flow for the Amazon river (cubic meters per second) indicates the volume of water that passes a given area in the river at any second. To illustrate how much 220,000 cubic meters is, the comic shows a car parked next to 220,000 cubic meters of water. 220,000 cubic meters equals a cube with an edge span of 60.4 meters. By comparison the 0.9 cubic meters (900 l) of goods that are shipped by Amazon.com seems very small (note that 900 liters of goods per second is still a lot). To illustrate this size, the comic shows an Amazonian fish (or possibly an Amazon river dolphin ) investigating the packages.
Iquitos and Manaus are cities near the source and middle respectively of the river; the title text suggests that it is shorter to have a package shipped between the two than let it drift downstream. "Minutes to skeletonize a cow" refers to piranha , an Amazonian predatory fish with a popular reputation of being capable of the mentioned act when hunting in groups. (It should be noted that, while not fictional per se, the legendary cow-killing piranhas had been starved beforehand by local humans.)
In 1599: Water Delivery Amazon.com takes the fight against the Amazon to a new level by delivering water within one hour; however, the Amazon River is not mentioned in that comic.
Round 14 Estimated outflow volume in cubic meters per second [A cube of water representing the outflow of the Amazon, with various marine life in it and people standing around it.] Amazon 220,000 [A pile of boxes representing the outflow of Amazon.com, dwarfed by the large cube of water next to it.] Amazon.com 0.9 Advantage: Amazon


Argument

Explanation:
A perpetual motion machine is a hypothetical device that is supposed to move infinitely with no external forces helping it, thus providing an unlimited source of energy. The existence of such an object would contradict the laws of thermodynamics, so perpetual motion machines are known to be impossible.
A conspiracy theory called Free energy suppression asserts that it really is possible to get infinite energy and special interest groups have worked to hide it. In the comic, Randall says that he posted to a forum dedicated to the idea back in 2004, and the thread is still active — it kept on going forever, like the perpetual motion machine they desire (in contrast with real attempts to build such a machine, which all stop quite soon). Of course, the reason the thread continues is that its advocates continue to add energy to it, in the form of comments. "Hot air", if you will.
The second law of thermodynamics states that the entropy of an isolated system never decreases. See this video about entropy . Thus, even if you could build a perpetual motion machine, you wouldn't be able to use it to produce energy that could be consumed by another device.
The three supposed comments show humorous forms of scientific ignorance :
Furthermore, the avatar being used by the second poster is that of a power strip plugged into itself, which is often jokingly thought of as a perpetual motion machine.
The title text refers to the fact that inventors have been trying to create perpetual motion machines, but have all failed to succeed. But given the fact that they all failed, each attempted perpetual motion machine stopped running at some point, while the search has never stopped.
[A page from a very long thread on " FREE Energy ~Forum~."] Thread: You're all crackpots who don't understand thermodynamics. [A bar above the comments:] Page 547 of 547 <<First <Prev 1 2 3 ... 545 546 547 Poster 1 [Default face icon]: No, idiot, only the north end of a magnet increases entropy. The south end decreases it. Poster 2 [Power strip plugged into itself icon]: I wiki'd this "First Law" and I don't see the issue. My device isn't a robot and doesn't harm humans. Poster 3 [Person with a large structure behind them icon]: What if we trick the government into only suppressing the left side of the flywheel? Ironically, the argument I started on a perpetual motion forum in 2004 shows no signs of slowing down.