Endangered

Explanation:
The endangered species list (also known as the IUCN Red List ) is a system for categorizing species based on "level of extinction". This list is primarily focused on macroscopic organisms such as animals and plants, as it is these organisms whose extinction is easiest to quantify, and on which most conservation efforts focus. Generally, it is a serious concern when a species is listed on the endangered species list, as this indicates its extinction could be at hand. Ponytail , Cueball , and Megan in this comic are scientists who maintain an endangered species list of microscopic pathogens. People generally want harmful pathogens and parasites to go extinct, [ citation needed ] unlike harmless plants and animals, so each species added to the pathogen endangered species list is a cause for celebration rather than concern, and the characters in the comic indulge in this celebration by sarcastically pretending to be upset about the potential for pathogen extinction, while in reality being excited about the possibility.
The title text mentions some of the species on the list, including polio and Guinea worm disease - diseases that have historically sickened and killed many people but are currently being eradicated due to worldwide efforts - the former, famously, through vaccination, and the latter through education and prevention techniques. As their eradication proceeds, they become more and more endangered of extinction, and thus earn their place on the list. The title also mentions a much less important pathogen, namely a certain strain of an enterovirus , also known as a stomach flu, which unlike polio and guinea worm is likely only to cause temporary discomfort, not death or long-term disability, in infected people. However, the strain in question infected every member of the lab maintaining the list, and as a result of their personal negative experience with it, and the spiteful feelings that resulted from that experience, the characters will celebrate its extinction as much as that of polio, and have accordingly added it to the list.
Randall was most likely inspired by this article about different influenza strains. Influenza causes the yearly flu, which infects 5–15% of the global population annually and causes 3-5 million severe cases worldwide.
The bitter irony here is that much recent scholarship has described links between parasite biodiversity and ecosystem-wide, indeed planet-wide, biodiversity . In a few cases, if preserving and expanding biodiversity are seen as good things, then preserving and expanding biodiversity of parasites is a good thing, the one not being possible without the other. Parasites and disease agents, arguably, are classes of predators, and their removal can help establish a superpredator, the actions of which can catastrophically drive down biodiversity. Humans, released from predation by a large percentage of formerly-effective microbial predators, through the introduction of penicillin and other antibiotics plus other elements of 'heroic medicine', sanitation, etc., have arguably become such a superpredator , and one that is mediating a loss of global biodiversity that may become the largest single species-extinction event in the history of planet Earth.
There also seems to be some evidence that infections with influenza viruses increase the chance of a heart attack. For instance regular flu shots reduce the risk of heart attacks . Thus the fact that we are "heartbroken" when B/Yamagata goes extinct could be sarcastic since we might suffer less from broken hearts.
[Ponytail stands facing Cueball and Megan in front of a poster board.] [Ponytail is pointing a stick to the board reading "Current List" with bullet points beneath.] [The first bullet reads Influenza B/Yamagata.] [Four further bullet points follow, which are left indistinct.]
Ponytail: Influenza's genetic diversity has declined during the pandemic, and the B/Yamagata lineage is at risk of extinction. Ponytail: Which would be such a shame. Megan: Yeah, I'm sooooooo worried about it. Cueball: We'd be just heartbroken!
[Caption below the panel]: When a pathogen that scientists really don't like is close to disappearing, it gets added to the sarcastic endangered species list.


Comet Visitor

Explanation:
Comet C/2014 UN 271 is a large comet that was discovered in 2014 almost as far from the Sun as the orbit of Neptune, and it will reach its closest approach in 2031, near Saturn's orbit. It's an Oort Cloud comet, with a period of more than 4 million years. Since modern humans ( homo sapiens ) evolved about 300,000 years ago (although tool-making ancestors were around about 2.5 million years ago), the last time it was among the planets was indeed long before humans evolved.
When a long-period comet comes into the inner Solar System, it's often figuratively called a "visit". But Megan and Cueball treat this more literally (or perhaps more sarcastically). Just as one usually neatens up their home when they're expecting guests, to make a good impression, they realize they need to clean up the Earth and its vicinity in preparation for this "visitor". Cueball starts handing out assignments -- he'll clean up the Pacific Garbage Patch , and suggests that Megan take care of all the debris in orbit .
Cueball and Megan also make notes to sweep up the lunar footprints that NASA astronauts left on the Moon during the Apollo missions and put away the Mars rovers . It's also common for people expecting visitors to put various objects out of view with the intention of returning them to their normal place after the visit, usually because the objects are considered unsightly that under normal circumstances is outweighed by the convenience of being out in the open.
However, since the comet will not come anywhere close to Earth and Mars, all this hardly seems necessary; it would be like cleaning up your home because the President or some other dignitary will be visiting your town. In addition, while a dignitary would theoretically be able to see one's house, although comets have tails , they do not have eyes, [ citation needed ] so they would not be able to perceive any difference between Earth before and after tidying up (even if the nucleus had an eye, it would not be able to see because it is in a coma ). Furthermore, sweeping footprints in the Moon, that Cueball sees as a way of tidying up, would be seen as destroying an invaluable archaeological sites by NASA and other people .
Alternatively, Megan and Cueball aren't "cleaning up" for a visitor as one might do if the visitor was a friend of theirs.  They're hiding themselves and contraband as one might do if they were worried the police were visiting. Or more likely in this context that it could be an alien visit, and they would like to make it difficult to spot the human civilization from space. In that case they might need to shut down all light in every big city on Earth as well.
The title text debunks the claim that the Great Wall of China is the only human-made structure visible from outer space ; in fact the Great Wall cannot easily be distinguished from space (as it is very long but not wide), but some other human constructions such as the Pyramids can (and cities are easily visible at night because they emit light).
[Megan sits at a desk in front of a computer, looking to the left off-panel and pointing at the screen] Megan: Have you seen this big comet, C/2014 UN271? Megan: It'll pass near Saturn's orbit in 10 years.
[In a frameless panel, Cueball stands behind Megan, who is now looking at the computer and typing] Cueball: Wow, look at the orbital period. Megan: Yeah, it hasn't been to this part of the solar system since humans evolved. Megan: At least.
[Cueball starts running off-panel, holding his finger in the air. Megan looks towards him with both arms resting on the back of her chair] Cueball: Well, we definitely need to tidy up. I'll start on the Pacific Garbage Patch, you tackle orbital debris. Megan: What about the moon footprints? Cueball: Sweep them up. Collect the Mars rovers, too! Cueball: We can put them back once it's gone.


Air Travel Packing List

Explanation:
This comic is another in a series of comics related to the COVID-19 pandemic .
The comic is about a proposed air-travel packing list, and the humor stems from the fact that many people have not been flying during the pandemic, and thus they might have forgotten what to pack. So Randall is so kind as to provide a packing list with 20 items. However, apart from the first item, the rest is not something you would or even should normally bring on an airplane.
Many of the items are already found on passenger airplanes, some items would seem like they could be useful on a plane, while others could actually be useful in case of a plane crash (but only if you survive), while many others would be counter-productive to safe air travel, even in the event of a crash. Below in the table is a quick summary of each item.
The title text references the idea that there is a trumpet for each passenger provided by the airline, which is item number 16 on the list. This items also states that you, because of the COVID-19 pandemic, should remember to bring your own mouthpiece for the trumpet as a safety measure.
The trumpet idea is then combined with the common debate regarding reclining your seat in airplanes. About half of the people think that reclining is rude as it takes up the space of the person behind you. The other half think that seats recline for a reason and the person in a seat has the rights to the space behind them. See for instance this video about such a debate. Reclining a seat has resulted in actual physical fights on board airplanes.
Here it seems that Randall sides with the anti-recliners, although maybe only in the context of the comic, because he states that reclining would prevent him from playing his trumpet, as the seat hits the bell of the trumpet. The person in front could certainly argue that playing the trumpet behind them would be very annoying, to which Randall could reply that because the trumpet is provided by the airline, he has the right to play it. This would add a new layer to the debate. This could also be Randall's way of arguing against the right to recline a seat, just because it is possible.
[A lists of 20 items is given in two columns with 10 items in each. Each item is preceded by a checkbox. Most items only take up one line, but in the left column two items take up two and in the right one item take up three, so they take up the same space. Above is a large heading, with an explanation beneath it.] Air Travel Packing List If you haven't flown in a while, you might not remember what you need to bring. Use this handy checklist to pack!
[Left column:] ☐ Seat cushion ☐ Parachute ☐ Wing glue ☐ Air horn ☐ Sextant ☐ Nose plugs and goggles for pressure ☐ Airplane shoes ☐ Navigation crystal ☐ Spare batteries in case the plane runs out ☐ Birdseed
[Right column:] ☐ Homing beacon ☐ Meteorite antidote ☐ USB wing connector ☐ Emergency siren ☐ Spare flaps ☐ Mouthpiece (Pandemic restriction; airlines still provide the trumpet) ☐ Luggage ballast ☐ Flag (International flights) ☐ Decoy tickets ☐ Keys to the plane


TSP vs TBSP

Explanation:
This is another one of Randall's Tips , this time a Cooking Tip.
This comic plays a joke on the common liquid measurements of teaspoons (tsp) and tablespoons (tbsp), which are commonly confused. In the US, a teaspoon is defined as 4.9 ml (0.18 imp fl oz; 0.17 US fl oz) while a tablespoon is defined as 14.8 ml (0.50 US fl oz; 3 tsp).
It also plays a joke on metric prefixes (based on powers of 10) versus binary prefixes (based on powers of 2), which are also a common source of confusion (see also 394: Kilobyte ). In the International System of Units (SI), T (for tera- ) signifies a multiplier of 10 12 (that is, 1 000 000 000 000), while Ti ( tebi- , for terabinary ), and not Tb, is an ISO standard binary prefix meaning 2 40 (that is, 1024 4 = 1 099 511 627 776).
If "spoon" is understood as US teaspoon, then one teraspoon will be 4 928 922 cubic meters (1.302 billion US gallons or 3996 acre-feet) and a binary teraspoon will be 5 419 407 cubic meters (1.432 B gal or 4394 acre-ft). If the US tablespoon is taken as base unit, a teraspoon will be 14 786 765 cubic meters and a binary teraspoon 16 258 220 cubic meters – roughly equivalent to six thousand Olympic-size swimming pools or slightly more than six times the volume of the Pyramid of Giza. All these units have fairly limited uses in cooking. [ citation needed ]
The title text is a play on a lyric from the Alanis Morissette song " Ironic ": "It's like ten thousand spoons when all you need is a knife." Randall changes the line to "teraspoon" and "kilonife". The "kilonife" comes from knife being interpreted as "nife" with a k prefix – k being the SI symbol for kilo- –, in a similar vein as taking tsp for "teraspoon". "Nife" is a geophysical name for Earth's core, thought to be composed of nickel and iron, and hence the word comes from the chemical symbols Ni (nickel) and Fe (iron).
Cooking tips: tsp vs tbsp [left column:] Tsp Teraspoon 1,000,000,000,000 (10 12 ) spoons
[right column:] Tbsp Binary tsp 1,099,511,627,776 (1024 4 ) spoons


New Nobel Prizes

Explanation:
The Nobel Prize is a set of prizes awarded in memory of Alfred Nobel to, "those who, during the preceding year, have conferred the greatest benefit to humankind."
In this comic a Nobel prize is being awarded for the discovery of two new Nobel prizes. This parallels Nobel Prizes awarded for the discovery of new elements . However, unlike elements, Nobel Prizes cannot be discovered. [ citation needed ]
The comic suggests that the doctor, presumably a social psychologist and the world's top expert on Impostor Syndrome , being awarded the prize came up with the idea of "discovering" Nobel Prizes, and no one can figure out how to stop awarding them to her.
In reality, the categories were established by Alfred Nobel's will for contributions or discoveries in the fields of Physics, Chemistry, Physiology or Medicine, Literature, and Peace. In 1968, Sweden's central bank funded an award for economics in honor of its 300th anniversary that is also colloquially called the Nobel Prize in Economics . While there is currently a petition to add a Nobel prize for contributions to environmental conservation, it would presumably also need external funding, although the decision process is unclear.
The title text is a play on the Nobel Prize in Physiology or Medicine , insinuating that the Nobel Assembly (the group in charge of awarding Nobel Prizes) has become so desperate to stop Doctor Adams that they have decided to award a Nobel Prize to anyone who can make her stop 'discovering' new prizes. The joke also plays on the name of the said prize, because as of the writing of this comic the Nobel Prize in Physiology or Medicine is the only Nobel Prize with two subjects (i.e. with "or" in the title). This may also be a jab by Randall at the fields of Physiology and Medicine, as poking fun at other disciplines is a recurring theme on xkcd. [ citation needed ]
This comic was published on the Monday the week following the announcements of the 2021 Nobel Prize recipients.
[Megan stands at a podium on a stage, facing right. Behind her is a screen showing eight Nobel Prizes. Ponytail is approaching the front of the stage while waving.] Megan: And all eight Nobel Prizes for the Discovery of New Nobel Prizes have been awarded to... Megan: *sigh* Megan: ...Doctor Adams, again , for the discovery of two new Prizes. Dr. Adams: Thank you, thank you!
[Caption below frame:] We don't know how she started this and now we can't figure out how to stop her.


Flag Map Sabotage

Explanation:
The comic refers to a type of map that colors countries using the national flag designs; see here for such a map of Europe. Randall proposes a new flag specifically designed to troll such maps.  Most obviously, the flag includes a legend with multiple common flag colors to indicate random regional attributes.  Hence, the mere act of placing this flag on a map would cause people to misinterpret this legend as applying to the entire map, giving wildly false information about regions of other countries. This trick is reminiscent of 327: Exploits of a Mom , with Mrs. Robert's son Robert'); DROP TABLE Students;-- .
In addition to the legend, the flag consists of two red fields, one of which has an irregular-shaped border, the other of which is a straight line. The irregular shape is similar to a geographical border based on natural features (such as rivers and coastlines), while borders not based on such features tend to be straight lines.  Red is the most common color on national flags, so if any bordering country had red on their flag, it would risk bordering these red fields, confusing where the border lay (as well as designating the entire red region as "greater Delaware").  If this flag is intended for the USA (although the text mentions "our new country"), the red regions would be continuous with the red strips on both sides of Canada's flag and the red field on the right of Mexico's flag, disguising the border still further.
The title text refers to the flag of Belgium, which consists of three vertical stripes in the order (left to right) black, yellow, and red. The western part of Belgium would, according to the legend, be unexplored, while the eastern part would be Greater Delaware. The middle would therefore be a tornado zone separating the unexplored area from Greater Delaware. Depending on how the flags are aligned it might be possible to explore from the south, where the blue-white-red stripes of the French flag contain another piece of Greater Delaware that may be conveniently located to help said exploration. Exploring from the Netherlands (red, white, and blue horizontal stripes) is not viable as rebel forces are positioned between Greater Delaware and the unexplored region.
This is not the first time Randall has made a flag for a new country! See 1815: Flag
[A flag displays a white country-shaped area surrounded by a red field. Inside the shape sits a map legend.]
[Label of map legend] Map Legend [Bright blue rectangle] Disputed territory [Green rectangle] Newly independent [Blue rectangle] Demilitarized zone [Yellow rectangle] Tornado warning [Dark blue rectangle] Held by rebel forces [Red rectangle] Greater Delaware [Black rectangle] Unexplored
[Caption below panel] Our new country's flag sabotages those maps where geographic areas are colored in with flag patterns.


Unsolved Math Problems

Explanation:
Math has many problems that remain "unsolved." This is not simply a matter of finding the correct numbers on both sides of an equal sign, but usually require proving or finding a counterexample to some conjecture, or explaining some property of some mathematical object. Sometimes this might involve extending an existing proof to a wider range of numbers like reals, complex numbers, or matrices.
A concrete problem is one that is very obviously connected to a real world process, while an abstract problem is one which seems unconnected to actual problems. In modern math, many problems tend to be very abstract, requiring complicated notation to adequately state the problem in the first place, like many of the millennium problems . On the other hand, many unsolved problems are very concrete; for example, there are very many problems related to packing objects into spaces that are very difficult to solve although quite easy to state, such as the Collatz conjecture . Finally, Randall describes a third category of "cursed problems," that have strange, seemingly random behavior, such as the behavior of turbulence or the distribution of prime numbers.
In the first panel, Ponytail describes a weird abstract problem. Her description seems to be a meaningless jumble of terms that are either mathematical or just sound mathematical. And the mathematical terms are from disparate branches of mathematics: group theory, topology, and calculus.
Finally she asks whether the problem statement is ill-formed; considering that it's mostly gibberish, this may be true.
Many real unsolved math problems appear similarly abstract. One example is the Hodge conjecture , a Millennium Prize problem. It states "Let X be a non-singular complex projective manifold. Then every Hodge class on X is a linear combination with rational coefficients of the cohomology classes of complex subvarieties of X." These words may appear nonsensical to a layperson. And even to an expert, the question is `abstract'. (Given a specific manifold, even an abelian fourfold, how on earth do you determine if a given 2,2 class is a cycle?)
In the second panel, Cueball describes a concrete random walk problem, and then mentions that this somehow has applications in three unrelated fields. This is actually not uncommon. The Wikipedia article says that "random walks have applications to engineering and many scientific fields including ecology, psychology, computer science, physics, chemistry, biology, economics, and sociology. Walking randomly on a grid never visiting any square twice is known as a self-avoiding walk ." This panel may have been inspired by some of the tricky unsolved problems about self-avoiding walks. Many of these problems have to do with rigorously proving properties of random walks that have been guessed by physics intuition, so these problems are connected to physics. The part about the maximum number of points in a line is reminiscent of problems in combinatorial geometry, which often involve counting points lying on different lines. Python code simulating this situation can be found here: [1] . C++ code simulating this situation can be found here: [2] .
In the final panel, Megan is looking at a strange curve that seems to have no consistent pattern. At the bottom it's mostly straight, with a few little wobbles. In the middle it looks like a wild, high-frequency wave that suddenly bursts and then dies down. And the top is a spiral that looks like a question mark or a Western-style Crosier . She wonders if this could even be mathematical.
On one hand, considering the weird shapes that come from plotting some mathematical processes (e.g. the Mandelbrot set ), it could well be. For example the unsolved Riemann hypothesis , another Millennium Prize problem, concerns the properties of a weird and at-first-glance random curve .  In number theory, the term "cursed curve" has been used to describe the "split Cartan" modular curve of level 13, which resisted attempts for many years to compute its set of rational points .
On the other hand, the question if could even be mathematical suggests that this may indeed not be a mathematical symbol. The curve looks like the unalome symbol, which is a Buddhist symbol which represents the path taken in life, or the journey to enlightenment. It could be argued that this indeed represents an unsolved problem, although not a mathematical one - which might then be part of the humoristic meaning.
In the title text, the curve in the final panel is further explained based on the consensus of supposedly a group who has studied it and the procedure that generates it, commenting that "it's just like that" as their conclusion, which is really not an explanation at all.
The Three Types Of Unsolved Math Problem
[First box:] Weirdly Abstract [Ponytail stands in front of an equation.] Is the Euler Field Manifold Hypergroup Isomorphic to a Gödel-Klein Meta-Algebreic ε<0 Quasimonoid Conjection under Sondheim Calculus? Or is the question ill-formed? ⬙ℝ̇ℤ/Eℵ₅ [The Z is raised and underneath it is a double-ended arrow bent at a right angle. One points toward the R the other toward the Z. The ₅ is double-struck (𝟝) like the R and Z.]
Second: Weirdly Concrete [Cueball stands in front of a grid with 6 columns and 7 rows] If I walk randomly on a grid, never visiting any square twice, placing a marble every N steps, on average how many marbles will be in the longest line after N*K steps? Somehow the answer is important in like three unrelated fields. [The path starts in the 3rd row and 3rd column, a small circle indicates the start. It takes the path: North, East, North, East (a black dot representing the 1st marble is placed here, so N=4), South, East, South, South (2nd marble), West, South, West, North (3rd marble), West, South, South, South (4th Marble), West, North, West, West (this goes offgrid to the West. There is no visible line or marble outside the grid). The 1st, 3rd, and 4th marbles are colinear and there is a dotted line connecting them. The line's slope is 3.]
Third: Cursed [A Megan with unkempt hair stands next to a curve] What in God's name is going on with this curve? Is it even math? [The curve starts at the bottom of the screen, rises straight upward, begins to wobble left and right a little. It lists to the left and the left-right motion increases, then decreases. It begins a large counter-clockwise arc, spiraling inwards twice, then ends]


Clinical Trials

Explanation:
The comic begins with a simple process for adopting a new idea just by convincing people that it is a good idea. The joke is that this skips the important step of checking whether it actually is a good idea. That correction presumably comes about after ideas are adopted which sounded good but turn out to be harmful. The comic captions the addition of this checking step as "the invention of clinical trials".
The purpose of clinical trials in medicine is to make sure that a new medicine works and doesn't have serious side-effects. One example of the dangers of failing to make sure that it doesn't have serious side effects is thalidomide , which caused a lot of birth defects. In a clinical trial, the effect of a treatment is compared to the effect of a placebo, or an existing treatment, to make sure it actually has a beneficial effect. (Earlier trials establish that it is even a viable candidate for testing and establishing possible dosages/regimens that can then be carried forward to a treatment (Phase III) trial.)
Before the invention of clinical trials, people generally didn't know, or at least had no way of confirming, whether medicines actually worked. Although many herbs and medicines were effective, others were no better than a placebo, and some medical treatments such as trepanation and bloodletting not only had no benefit (except for a very few rare conditions) but were very likely to be harmful. Those treatments that did work at all were mostly those that had been tried (for whatever reason ) and just happened to be useful, but others had neutral or even adverse effects, but still managed to not be so dangerous that subsequent recoveries from the original ailment—regardless of (or despite!) dangers inherent in such treatments—were taken as proof of their efficacy.
Similar to more recent examples, some earlier treatments may have been gradually discovered to help a particular condition only by noticing beneficial side-effects when consumed for sustenance or for unrelated medical 'guesses'. However, they also remained without the full scientific rigour so long as it remained a 'traditional remedy' with at best an oral tradition across many disparate practitioners, and no consistent effort to formalise or test the falsifiability of any findings.
At the time that this comic was published, the world was in the middle of the COVID-19 pandemic , which made the existence of clinical trials more relevant to the public, who waited eagerly for what sounded like good ideas to get through clinical trials and available to the general public… or fail clinical trials and not do that. During this frustrating wait, many unscientific claims have been made that various drugs or non-drug treatments are cures for COVID-19, making it difficult to convince believers to get real treatments. On the other hand, many people were skeptical about COVID-19 vaccines which were made available to the public for emergency use before the clinical trials were finished, or had concerns about whether the clinical trials were rushed or otherwise flawed due how quickly they were conducted compared to the traditional speed for vaccine development and approval.
In the title text, "Standard of care" refers to the previously accepted practice which a new medicine needs to be compared against. Because the original 3-step "standard of care" in this comic didn't include clinical trials before their adoption, we didn't need to do any testing in order to decide to start using them. If we had had them as the standard of care, then we would have had to perform tests before we added a step and it would have taken longer. This assumes that the process itself is subject to the same scientific rigor as medical treatment; in practice that would be more of a political change that is still not tested.
This comic can be viewed to criticize several extreme political proposals that are obviously bad ideas to most people, such as abolishing the nuclear family, making gay marriage illegal, blocking the development of renewable energy sources and defunding the police. People tested the latter in Seattle, and the test didn't go well .
1. Come up with new idea 2. Convince people it's good
[Scrawled in red as an afterthought, an arrow inserting it between item 2 and the original item 3] 3. Check whether it works
3. [Now scribbled over and amended to "4."] New idea is adopted
[Caption below the panel] The invention of clinical trials


Dark Arts

Explanation:
White Hat has presumably just asked Cueball to perform some task involving filesystems . Cueball responds with an exceptionally melodramatic monologue, referring to the subject as "dark arts" and stating he'd rather not have anything to do with them. This is reminiscent of a fairly typical scene in fantasy novels, superhero movies, etc: a person with supernatural powers explains they prefer not to use them, as their use is likely to have negative effects that outweigh the positive ones. Often this is tied to a tragic backstory of the character, where the use of their powers previously caused them or someone close to them much suffering.
The humor of the comic comes from the parallel drawn; it seems unlikely that knowledge of filesystems could have negative consequences on the scale of, say, leveling a city, so the comparison is hyperbolic. However, much of today's infrastructure does depend on legacy systems that can be very overly complex to work with, having weathered aggressive political conflicts and short corporate deadlines for decades now. An example is the recent shutdown of the pgp keyserver network, or how the developer of the fastest linux filesystem built (reiserfs) was imprisoned for murdering his wife right before it could be merged into linux. Still, this joke is in a similar vein to comics like 349: Success , in which Cueball's relationship with technology is shown to have a potential for disaster far exceeding that of a normal person's.
A filesystem is the part of a computer's operating system that handles the organization of data in persistent storage, usually splitting it into files and directories. It can be a very complicated piece of software. Because of this, it is easy to make mistakes in advanced usage, and because it controls practically all data on a given machine, mistakes made can have serious consequences (e.g., loss of data). These properties of filesystems are likely why Cueball is reluctant to mess with them.
ext4 is a popular filesystem used with the Linux operating system kernel.
Hardlinks allow two filenames to refer to the same underlying file or directory. These can be particularly tricky to use, as in nearly all respects they look like regular files, but modifying them can have effects that are not immediately obvious (e.g., changing what one filename refers to, the other will not remain consistent). Hardlinks and their misuse have been referenced in xkcd before, as in 981: Porn Folder .
The title text hints at an experience Cueball or Randall had (his own "tragic backstory", if you will), involving hardlinks on ext4. He thought he had found an ideal use case for them, one which presumably avoided most of their pitfalls, but still, six months later, ended up having to troubleshoot some inscrutable bug arising from his decision.
Javascript is a programming language most often associated with web pages. As such it is not usually interacting directly with a computer's filesystem, since allowing arbitrary websites to access the filesystem is widely considered an extremely bad idea [ citation needed ] . It is possible to run Javascript directly outside of a browser – in which case it does have access to common filesystem operations, and even theoretically to the internals of the filesystem – but since it is a high-level language with poor support for working with the data structures a filesystem uses, this would be a painful, "cursed" way to go about things.
A senior IT professional (nowadays fewer people need to know about such features) will be reminded of their own experiences and mishaps with non-trivial file system configurations.  Beyond hardlinks, filesystems may have a number of features a normal user or even an admin are not aware of. Such features are prone to bugs, poor documentation, or poor integration with other system tools.
For example:
"In another age" might refer to the fact that detailed file system manipulations were common in the days when developers were installing, configuring and managing operating systems and software on physical servers. When disk space was limited and network speeds were low, such manipulations saved space and time. Virtualization, containerization and deployment frameworks isolate developers and administrators from such low level details.
[Cueball and White Hat stand in a slightly darkened room, with a jagged circle of light centered on Cueball and light-reflecting onto White Hat's face. Cueball holds his arm out with his palm facing towards White Hat.] Cueball: Long ago, in another age, I mastered these dark arts. Cueball: But I now endeavor to live my life such that I never need them. Cueball: Their power leads only to ruin. [Caption below panel] My response whenever anyone asks me to mess around with filesystems


Censored Vaccine Card

Explanation:
This comic is another entry in a series of comics related to the COVID-19 pandemic , specifically regarding the COVID-19 vaccine .
The comic hinges on the sharing of vaccination card photos on social media as proof that the user has been vaccinated against COVID-19 (in this case, gotten a booster shot , a third dose of the vaccine). When people in the United States first started receiving their vaccine shots, a large number of them shared photos of the CDC vaccination proof cards that they received alongside the vaccines; it was enough of a trend that the FTC released an official statement warning vaccine recipients not to share photos , due to the cards containing personal identification that probably should not be made public.
The irony here is that Randall has " censored " (redacted) some impersonal lines, such as the instructions that are identical on all vaccination cards, and many easy-to-guess lines, while not censoring any of said personal information.
Considering the date of the 3rd dose (one day prior to the comic's uploading), it is likely that the blackouts in the last line are only covering whitespace.
Another possible reference here is to the practice of filing for FOIA requests that has been getting more popular in recent years, with sites like muckrock.com developing to support it.  These requests provide for citizens to view the contents of government files, but the files first go through a process of redaction via solid black rectangles.  The information that is redacted can seem random, ridiculous, and frustrating, and be a source of legal action.
The caption indicates that his intention is to "seem more mysterious". This is best exemplified by the blanking of most of the word "clinician" to leave the acronym " CIA ", referring to the US government agency known for its frequently "mysterious" (classified) activity, as well as its liberal use of redaction like that in the comic.
The "19" in COVID-19 is systematically censored in the comic. This is humorous because currently COVID-19 is the only thing that could be meant by "COVID-[anything]", and so the redaction is pointless. This may also be intended, in the interest of mystery, to imply some future outbreak of a similar disease (given an identifier based on the year of its inception).
The sentence at the top of the card, which appears once in English and once in Spanish, has equivalent portions redacted in both languages:
This is the first comic including a sentence (or, given the censorship, at least a good portion of one) in Spanish.
CVS Pharmacy is a pharmacy chain in the US which provides COVID-19 vaccinations.  CVS #05309 is in Pineville, LA, while Randall lives in Massachusetts; it is not clear why he would have received his first vaccine dose in Louisiana.
The title text comments on the "Provider or clinic site" of the second dose on the card. Where the word "pharmacy" appears in the previous row (and would be on a real card), it is censored in the comic. The most reasonable assumption is that the word is still "pharmacy" and that Randall has simply chosen to redact that instance for some reason, but the title text humorously implies that it was in fact some other CVS-related venture where he got his second dose, for instance a "CVS parking lot" or perhaps an anti-submarine warfare carrier .
CVS's parent company, CVS Health , does have other enterprises with compatible names: CVS Caremark and CVS Specialty . However, neither of these provide COVID-19 vaccinations.
Randall's patient number is the 2nd to 9th digits of the fractional part of the decimal expansion of pi inclusively: 41592653.
The lot numbers of the first and second doses allude to two numbers that appear frequently in Star Wars and other works related to George Lucas: 1138 , and 2187 . The lot number of the third dose is the Ramanujan-Hardy number .
The Clinician number for the first shot is the last 4 digits of the phone number for "Jenny" 867-5309 , which has been entered into communication technology by a massive number of people.
Given the reasonable assumption [ citation needed ] that the partially censored year relates to the twentieth century, the date of birth on the card corresponds to that given in the acknowledged timeline for Randall. The censorship of that specific part of his date of birth might be related to the fact that the number "19" has been systematically redacted on the card. Another interpretation is that Randall is implying he is either over one hundred years old or a time traveler, although neither is likely to be true. [ citation needed ]
[Profile picture of a Cueball's head and shoulders, with unreadable lines of text to the right.] Check it out, I just got my booster!
[Picture of the U.S. COVID-19 Vaccination Record Card attached on a media post. The card includes pre-printed information in black and handwritten information in blue, the latter indicated here by bold text. Some of the text has been blacked out, indicated here by "[censored]".]
COVID-[censored] Vaccination record card [At the upper right of the card appears the logo of the U.S. Department of Health and Human Services, a stylized eagle surrounded by the words "Department of Health & Human Services USA", although those words are not legible in this drawing. Next to that appears the logo of the Centers for Disease Control and Prevention, a shaded box with the letters "CDC" and the words "Centers for Disease Control and [censored]" below it.]
Please keep this record card, which includes [censored] about [censored]. Por favor, guarde esta tarjeta de registro, que incluye [censored] [censored] sobre [censored].
Munroe Randall
Last Name                     First Name
10-17-[censored]84 41592653
Date of birth                 Patient number
[A table fills the remainder of the card. It has four columns and five rows. The first row gives the column names:] Vaccine. Manufacturer lot number. Date. Provider or clinic site. [The rest of the rows have been filled out. Each "date" cell also includes pre-printed "MM DD YY" below the line where the date is written.] 1st dose COVID-[censored]. Pfizer ER1138 . 04 / 01 / 21 . CVS Pharmacy Clinician #5309 . 2nd dose COVID-[censored]. Pfizer ES2187 . 04 / 22 / 21 . CVS [censored] [censored]. Other. 3rd dose [censored] FH1729 . 10 / 21 / 21 . [censored] [censored] [censored] CIA [censored]. Other. [censored]. [censored]/[censored]/[censored]. [censored].
[Caption below panel:] Security tip: To seem more mysterious, try censoring only non -identifying information.


Slope Hypothesis Testing

Explanation:
"Slope hypothesis testing" is a method of testing the significance of a hypothesis involving a scatter plot.
In this comic, Cueball and Megan are performing a study comparing student exam grades to the volume of their screams. Student A has the worst grade and softest scream, but Student B has the best grades and Student C the loudest scream. A trendline has been plotted, indicating a positive correlation between grades and volume...but the p-value is extremely high, indicating little statistical significance to the trend. P-value is based on both how well the data fits the trendline and how many data points have been taken; the more data points and the better they fit, the lower the p-value and more significant the data.
Megan complains about the insignificance of their results, so Cueball suggests having each student scream into the microphone a few more times. (The three students are still there as they can be seen behind them. The three students look like schoolkids; one of them is Science Girl .)
Having the students scream again will not help though, because it only provides more data on the screaming without providing more data on its relation to exam scores, and is a joke around poor statistical calculations likely made in the field today. The p-value is incorrectly recalculated based on the increased number of measurements without accounting for the fact that observations are nested within students. Each student has exactly the same test scores (probably referencing the same datum as before) and have vocal volume ranges that don't drift far either (each seems to have a range of scream that is fairly consistent and far from overlapping). Megan is pleased by these results, but Cueball belatedly realizes this technique may not be scientifically valid. Cueball is correct (presuming that they are using simple linear regression). A more appropriate technique would account for the non-independence of the data (that multiple data points come from each person). Examples of such techniques are multilevel modeling and Huber-White robust standard errors.
Measuring data multiple times can be a way to increase its accuracy, but does not increase the number of data points with regard to another metric, and the horizontally clustered points on the chart make this visually clear. A more effective and scientifically correct way of gathering data test would be to test other students and add their figures to the existing data, rather than repeatedly testing the same three students.
Common statistical formulae assume the data points are statistically independent, that is, that the test score and volume measurement from one point don't reveal anything about those of the other points. By measuring each individual's scream multiple times, Cueball and Megan violate the independence assumption (a person's scream volume is unlikely to be independent from one scream to the next) and invalidate their significance calculation. This is an example of pseudoreplication. Furthermore, Megan and Cueball fail to obtain new test scores for each student, which would further limit their statistical options.
Another strange aspect of their experiment is that the p-values obtained during a typical linear regression assume there is uncertainty in the y-values but the x-values are fully known, whereas in this experiment, they are reducing uncertainty in the x-values of their data, while doing nothing to improve knowledge of the y-values.
Moreover, even if the new data were statistically independent, this still appears to be a classic example of "p-hacking", where new data is added until a statistically significant p-value is obtained.
In current AI, there's a push toward "few-shot learning", where only a few data items are used to form conclusions, rather than the usual millions of them.  This comic displays danger associated with using such approaches without understanding them in depth.
Additionally, a common theme in some research is the discovery of correlations that do not survive independent reproduction.  This is because randomness with too few samples produces apparent correlations, and Randall has repeatedly made comics about this hopeful error (see 111 , 925 and 882 among others).
In the title text, Megan and Cueball are trying to yell over each other, asking each other to speak up so they can be heard, presumably because they are having trouble hearing from the yelling experiment.  Or possibly they have trouble speaking audibly because they score poorly on statistics exams.
[Three points are labeled "Student A", "Student B" and "Student C" from left to right in a scatter plot with axes labeled "Stats exam grade" (60-100) and "Scream loudness (decibels)" (86-94) with a trend line. Student B has the highest exam grade, followed by Student C and then Student A.] [A line goes from the trend line to a box containing the following:] β=1.94 p=0.586
[In a frameless panel, Megan reads a piece of paper while facing Cueball while three students look at them from the background.] Megan: Darn, not significant. Cueball: We need more data. Have them each try yelling into the mic a few more times.
[The same scatter plot as in the first panel except with more points for each of the students with slightly different decibel values, and the text in the text box changed to:] β=1.94 p=0.037* *Significant!
[Similar panel to the second one] Megan: Perfect! Cueball: Are you sure we're doing slope hypothesis testing right?


Retractable Rocket

Explanation:
This comic documents another of Beret Guy 's absurdist ventures . He explains to Megan that "we" (possibly his company ) are testing their new "retractable" rocket.
Reusable rockets are a growing industry, as they are more economically viable in the long run – though technically much more difficult to operate – than rocket boosters that are just discarded after use (which have been standard throughout the majority of space-faring history). Thus, Megan is understandably confused about Beret Guy's assertion that theirs is "retractable", asking if he misspoke. In typical fashion, he assures her that he did not misspeak, with a single "No" without further explanation.
They proceed to watch the rocket "launch", proving that it is indeed retractable . In fact the rocket does not launch, but merely extends – apparently all the way to the International Space Station (ISS), a height of over 400 km (over 250 miles) – before retracting, as promised, to its original position. The top part, with the astronauts in it, has been left in space. Presumably, it is docked to the ISS, as the crew onboard the ISS say hello to them in panel 4.
Of course, it would not be possible to extend anything this far. [ citation needed ] The top would need to be moving very fast compared to the bottom part, or it would bend westwards and break, and even with the strongest material a fully extended, very thin, presumably, hollow structure with a payload on top would buckle very soon after extension began. Also, the ISS moves at 27,600 km/h (17,100 mph) compared to the ground under it, making an orbit in about one and a half hours. So making the tip follow this long enough to dock would be even more impossible.
Beret Guy's retractable rocket has more than a few similarities to a space elevator which has been discussed in real life. The chief difference is, a space elevator is only extended once (and most likely this would be down from space, not extended upwards), and never retracted unless it needs to be dismantled. Randall has referenced space elevators in 697: Tensile vs. Shear Strength . A more similar theoretical means to attain orbit is that of the space fountain . He has also examined the problems of a solid metal object extending through the atmosphere in a what-if .
The current method of sending rockets into space requires huge amounts of fuel, and the more fuel you attempt to carry, the heavier the rocket, leading to more fuel being required, etc. ( Tsiolkovsky rocket equation ), which makes the current method inefficient.  Alternate methods are being explored, such as using a slingshot ( SpinLaunch had a successful test flight of a smaller scale launcher just days before this comic was published, probably the influence for this comic), theoretical space elevators , or this comic's impossible retractable rocket idea, all of which would leave the majority of the "fuel" requirements on Earth or elsewhere rather than having to carry heavy fuel with the rocket.  The only fuel carried might be minimal amounts for course adjustments once in space rather than large amounts used to get there.  However, many of these methods are less flexible than rockets; the space elevator, for instance, operates on the basis of constant angular velocity relative to the Earth's axis of rotation, meaning that it cannot launch payloads directly into low-earth orbit, polar orbits, or many other orbits frequently used by satellites for their desirable characteristics, and satellites intended for these orbits might still need to carry considerable amounts of fuel, even if less than that required to launch directly from the ground.
The title text parodies the 'old' single-use boosters. It appears that the predecessors to the 'retractable rockets' were capable of controlled extension only. Once they had lofted the payload to orbit, they were then allowed to fall over, destroying them in the process so they could not be used again just like booster rockets. However, if a 250 mile/400 km high construction just fell over, it would be much more difficult to avoid other damage, than to the rocket (booster), than for just a few small booster rockets falling out of the sky. [ citation needed ]
This comic was released four days before (and possibly refers to) SpaceX's Crew-3 mission to send astronauts to ISS with a reusable rocket on 31 October 2021.
[Beret Guy and Megan is talking. Behind them near the horizon is a tall rocket on a launchpad.] Beret Guy: We're testing our new retractable rocket. Megan: You mean reusable? Beret Guy: No.
[A zoom in on the launchpad and rocket. It has the appearance of having a long first stage, a second stage with slightly wider fairing and an Apollo-style capsule with escape-tower atop it all. There is a directionless speech-bubble at the top depicting a count down voice.] Count down: Three...Two...One...Liftoff!
[Same view as before, but while the base of the rocket-stack remains stationary, the first stage is apparently elongated, with a hint of a bend to the right, to raise the total height to which the upper-stage and capsule assembly reaches almost to the top of the panel.]
[In a wider panel, with the base to the left, the first stage is now elongated far enough to disappear off the top of the center of the frame, thus clearly bending to the right. Two peoples voices are indicated as coming from the space capsule far above, as it reaches it destination.] Voice 1: Hi, welcome to the ISS! Voice 2: Hello!
[The final panel shows the same view as in the third panel. The first stage is now retracting, and has similar length as in the third panel, but the capsule is no longer atop the 'second stage' fairing. Four movement lines above the top of the retracting rocket indicates that it is returning back to the original position.]


Common Cold Viruses

Explanation:
This comic is another entry in a series of comics related to the COVID-19 pandemic .
In this strip, Megan and White Hat are listening to Cueball explain his newfound interest in the various different viruses that cause the common cold , which is an umbrella term used to describe the mild-to-moderate symptoms these viruses all cause.
Megan expresses curiosity as well, and White Hat suggests he could get a DNA sequencer to help. By the third and final panel, several years have passed. All three characters appear to be ill, perhaps even as a result of now purposefully infecting themselves with chosen diseases. Whether deliberately or 'naturally', they do seem to have by now encountered a respiratory syncytial virus (RSV) and various types of rhinoviruses , and are now describing their experienced symptoms with terms similar to ones used in wine tasting (e.g. "bouquet" is a term used in wine tasting; "nosefeel" is a parody of the wine-tasting term "mouthfeel", etc.).
This strip follows the theme of 915: Connoisseur , making fun of the fact that people can form strong opinions and preferences on pretty much anything if they spend enough time and attention on it.  In this case, despite the fact that the symptoms of these viruses are almost universally considered to be unpleasant, the characters appear to have developed an appreciation for the subtle variations.  A similar phenomenon is referenced in 1095: Crazy Straws .
The idea of intentionally infecting a person with a disease is a trope in multiple Speculative Fiction stories. For instance, Iain M. Banks' Culture series , set in a world where all diseases are eradicated or treatable, includes story lines where persons deliberately infect themselves with viruses to experience the symptoms.
The title text references the H1N1 swine flu virus, which was the disease at the heart of the 2009 swine flu pandemic . It also further expands on the wine tasting comparison – connoisseurs often consider the environmental conditions of the growing season the grapes came from as an important factor in the quality of a given wine, so certain years may be considered better than others.  Since 2009, less severe forms of H1N1 influenza have become one of the standard variants in annual flu seasons and a perennial in the influenza vaccination mix.  From the influenza strain's perspective, 2009 was the year of breakthrough success for H1N1.
As access to community makerspaces, labs, and knowledge has spread, people have begun doing more things at home that were previously confined to industrial and academic research environments.  This was stimulated further during the onset of the pandemic, when communities became focused on helping offset overtaxed national resources.
[Megan, Cueball, and White Hat are standing in a group.] Cueball: COVID has made me so curious about colds. The next time I get one, I want to know which virus it is specifically. Cueball: A rhinovirus? RSV? Mild influenza? Or something weird like metapneumovirus?
[They begin to talk together.] Megan: How distinct are they? Could you learn to tell them apart? Cueball: See, I wonder! White Hat: I could get a sequencer from work...
[Caption above the panel:] Several years later... [In this panel, Cueball is sitting on the left, Megan is sitting on the right, and White Hat is standing at the far right. Megan is coughing, her hair frazzled. There is a tissue box in the middle, and discarded tissues lie on the ground.] Cueball: Ah yes, this one has the rich, full-bodied bouquet of RSV, but the heady congestion lends it a lingering rhinovirus nosefeel. Megan: *Cough* Megan: Quite right!


Wirecutter

Explanation:
Wirecutter is a product review website owned by The New York Times . Randall is parodying the website by having them "review" the 70 most popular religions . Product review websites typically make posts with the "best" X, e.g. "Best smartphones," or "Best laptops." These reviews are useful for consumers trying to choose among the wide variety of products available.
There are a wide variety of religions . However, unlike electronic devices, a person does not usually choose their religion; they are taught one during childhood and most remain in that religion their entire life. Changing religions is ( usually ) a significant life event. [ citation needed ] Many religions, including many variants of the three major Abrahamic religions promote exclusivity , and do not recognize other religions as valid. They emphasize the importance of specific practices or belief in specific creeds. Members of those religions might not recognize a reviewer as having truly "tried" their religion if their intent was always to move on to another.
A post "reviewing" religions is sure to stir up controversy, as many religious followers are passionate about their religious beliefs and believe their religion is best. Literal wars have been fought over the idea one religion could be superior to another, and it is not a wound most practitioners are willing to reopen any time soon. Moreover, religions are typically chosen for more fundamental reasons -- such as by comparing the likelihood that each religion makes accurate claims, or the efficacy of each religion in promoting an ethical life, or the connection a practitioner feels to the religion's rituals, metaphors, and images, or by privileging a preexisting cultural or family connection to a particular tradition -- not by comparing gimmicky features or price.
The title text mentions "budget" and "upgrade" picks, which are subcategories for reviewers - cheaper options and options that are good for upgrading your current product. Neither of these categories are typical categories for religions [ citation needed ] and could further anger their adherents. The association of religion and money could allude to various controversial topics such as tithing , indulgences , televangelism , or Prosperity theology .  Budget need not be just about money, it could also refer to the amount of time or effort involved.  (e.g., how much time is spent in religious activities, needing to learn a new language, etc.)  Some religious followers might be offended [ citation needed ] if their religion was picked in a "budget" category. The idea of a religion "upgrade" evokes the highly divisive concept of supersessionism among the major Abrahamic religions, which would be guaranteed to cause further outcry no matter which one of those the article would pick for the category.
[A New York Times Wirecutter article. There is the NYT logo and Wirecutter logo in the top left. Also in the top of the page is a search bar, a user account icon, and 7 "header" level hyperlinks with illegible text. The article title is as follows:] The Best Religion By Wirecutter Staff
[The words "Wirecutter Staff" are followed by illegible text presumably representing the date of the article. Below are icons for Twitter, Facebook, e-mail, and save.]
[The article's image depicts Cueball shrugging in the center of the picture with many question marks floating above him. The content of the article is as follows:]
What does it all mean? Our reviewers tried out over 70 of the most popular belief systems. Here's what they found…


Painbow Award

Explanation:
This comic makes fun of the badly selected color scales used in the figures for scientific papers by suggesting that the scientists picking them are in competition to use the most problematic scale. The title of the comic is a portmanteau of "pain" and "rainbow" suggesting a humorous name for terrible color scales.
The color scale here showcases a collection of unintuitive and unhelpful decisions. Starting from the top, white fades down into green, which then fades into red (passing through brown in the middle instead of yellow, indicating subtractive color mixing instead of additive color mixing, for no obvious reason). The red then turns back into green as the intensity decreases further. Red and green in close proximity make the energy levels hard or impossible to distinguish for those with protanopic color vision deficiency . This confusion is repeated at lower energy levels, where blue transitions to black and then back into white via a gray with a tiny tinge of blue. The highest and lowest recorded energy levels have the same color value, which is less than ideal. That Randall is aware of color blindness and the problems this causes has been revealed in other comics like this one 1213: Combination Vision Test .
Although it's possible (for someone with full color vision) to interpret data from this graph from context clues - the white that fades to green is high-energy white, while the white that fades to blue is low-energy white - there's no benefit to doing things this way, and a lot of downsides. Additionally, there are regions in the color scale where the color changes very rapidly, which creates the false appearance of an edge in what is likely a smooth function.
Because the color scale includes black, representing just over 20 unlabeled units, it is possible that the graph axes, labels, and perhaps even the comic's caption represent measured values. Because they don't blend continuously with the negative space around them, this appears unlikely.
Real-world analogues to the Painbow Award include radar meteorology charts, where different types of precipitation have different color schemes that can overlap and blend in confusing transition zones. In the field of data visualization, the CIELAB color space , perceptually uniform color spaces , or even more specialised scales have been developed to replace simple algebraic interpolation of red, green, and blue values.
The title text takes the concept of bad color combinations further, suggesting the use of navy blue , dark blue , and midnight blue for first, second, and third respectively. These are the names of three similar XKCD colors , and, as sighted readers will be able to see, there is very little difference between them [ citation needed ] . However, the choice of blue(s) may be a direct play upon the association of the Blue Riband (a.k.a. "Blue Ribbon") and/or Cordon Bleu (likewise, but this time direct from the French) awards, extended in common use for excellence across a much wider range of competitive fields.
For rosette-rewarded competitions (e.g. livestock parades, dog-shows, etc) the first prize ones are commonly blue (red for 2 nd and either yellow or white for 3 rd ), though it may not be logically obvious to someone unfamiliar with this, perhaps more used to yellow depicting the 'gold standard, first place' indicator or red as the most alerting hue in some other ranking situations. Where a depicted award schema is directly gold/silver/bronze-influenced, however, the gold and bronze 'metallic off-yellows' can sometimes be more confused with each other than with the mid-level desaturated 'silver'
[A figure of a graph is shown, the figure has a number as if used in a paper. The graph has two labeled axis but without any units given. The Y-Axis has 15 ticks of equal length, the X-axis has 21 ticks, with every fifth double the height of the other. The graph displays a messy shape with color gradients, with a bright spot to the right of the shape around the middle right part of the graph. This bright spot is surrounded by mainly green and red, with darker colors at the edge, and the rest of the graph white. On the right side of the graph there is a labeled bar with the color scale. To the right of this are numbers indicating what the color represents. The color scale begins at the bottom with white, then goes to gray/blue, to black, back to blue, to gray, to green, to dark red, to red which fades via brown in to green, from where it fades slowly from darker green to lighter green ending up as yellow before going back to white again at the top.] Label: Figure 2 Y-Axis: λ X-Axis: θ (phase) Scale label: Peak Energy 120 100 80 60 40 20 0
[Caption under the panel:] Every year, disgruntled scientists compete for the Painbow Award for worst color scale.


Snack

Explanation:
Many psychological studies involve participants being asked to make decisions under varying conditions, to determine how those conditions influence decision making. A common example is to give subjects a choice between eating a healthy snack (such as an apple) or a tasty snack (such as a cookie), which may be used as a simple proxy for whether they're prioritizing long-term health or short-term gratification. In most cases they are not made aware of the nature of the experiment, as knowing the premise of the study is liable to influence their behavior and alter the results. Instead subjects may deliberately be given a false impression of the purpose of the study, or they may be offered a choice under conditions where they're not aware that they're part of an experiment at all.
Examples of experiments like this are the Stanford marshmallow experiment and this study .
This sort of psychological study is most commonly done by universities, which means that using university students as subjects is generally the most convenient option. This means both that psychological studies tend to be heavily skewed towards the demographics of college students, and that university students have a pretty good chance of being invited to participate in a study at some point.
The joke in this strip is based on the premise that psychology majors are sufficiently aware of such studies that it would make them suspicious of any circumstances which could be part of a study.  If they've studied (or even conducted) such experiments, anything that reminded them of such a study could cause them to become suspicious. In Cueball 's case this is exaggerated into outright paranoia, and Ponytail is apparently playing on that to prank him, offering options that could easily be part of such an experiment just to spook him into suspicion.
Studies done on humans are subject to important ethical controls, particularly if the subjects are not fully informed of the study's purpose. "IRB" stands for Institutional Review Board , which is a committee (for example, at a university) which must approve such research to ensure that there's no significant risk of doing harm to the subjects of the study.
The title text jokes that graduate students have so much work to do that they are liable to forget to eat entirely and stereotypically too impoverished to afford adequate amounts of food; when presented with an offer of a snack, they don't ponder the implications or potential ulterior motives; they just eat it quickly and get back to work.
[Ponytail, holding a cookie up in one hand and an apple up in the other, addresses an alarmed Cueball. His alarm is shown by seven lines radiating away from his head, and he also holds his arms stretched out.] Ponytail: Hey, do you want a cookie? Or an apple? Cueball: Who are you!? Did the IRB approve this!? Is everyone here an actor!?
[Caption beneath the panel:] The best prank you can play on psych majors is just to offer them a snack.


Flinch

Explanation:
Cueball is performing a common physics demonstration in which a heavy ball is hung from a rope or cable. The demonstrator, or a volunteer, pulls the ball back until it's close to their face (possibly even touching it), then releases it, allowing it to swing, and then return. Due to conservation of energy, the ball cannot return any further than its original release point, making it impossible for the person to be struck by it. Because a heavy pendulum will tend to lose little energy on each swing (relative to its overall energy), it will come back very close to its original point, so the experiment creates a conflict between the instinctive desire to escape a heavy object flying at your face, and the theoretical knowledge that it won't harm you.
Megan is a physicist, who understands the principles of the experiment and claims she won't flinch, confident that it can't harm her.
Hairy is a biologist, and implies that he has no intention of avoiding the flinch reflex, as he trusts the automatic reflexes that the human body has evolved more than he trusts the premise of the experiment. In  both 755: Interdisciplinary and 1670: Laws of Physics , the same experiment is referenced. In the title text of the latter Randall makes a very similar argument as the biologist does here.
Ponytail , an engineer, replies that she doesn't trust Cueball to have hung the pendulum correctly.  Engineers are trained in science, but work with practical applications, and tend to be very aware that practice is rarely as simple as scientific theories might imply. Even if the physical laws are constant, the experiment might not go according to plan. For example, if the cable were to snap or come loose while swinging toward the subject, the ball could strike them in the body, or land on their feet.  If the cable is more elastic than anticipated, it could stretch unpredictably, once again striking someone.  If the anchor point is not stable, it could shift during the experiment, once again causing harm. Also if the ball is not released but pushed, or if the one releasing it leans forward after release they might get hit in the face.
The punch line basically makes the point that failure to trust the safety of an experiment doesn't necessarily imply a lack of scientific knowledge.  If you lack confidence in the design of an experiment, then it's not safe to assume that the laws of physics will protect you.
The title text shows a pre-med student's response. Pre-medical university courses have a reputation for being more intense and demanding than other undergraduate degrees, so the student is portrayed as being very stressed and time-conscious; showing little interest in the experiment itself, only in how it impacts their degree. In addition, medical students are commonly the subject of "interesting" medical experiments which may lead to long-term psychological and physical side-effects.
The student first asks if participating in the demonstration will count for a physics credit, implying that they're not willing to spend time on it unless it contributes to their academic requirements. They then ask if they can shorten the string to make the demonstration go faster. Shortening a pendulum does, indeed, cause it to swing faster, but the time saved would be less than the time necessary to make the modification, so the demonstration would not end sooner. Finally, they ask to do a variant where they deliberately get struck in the face, because they have a "thing for first aid training" immediately after. This would likely injure them, but the student is apparently willing to sacrifice their own safety and well-being in service to their academic career. It's not clear how this would help, although it could potentially help others learn first aid by having them practice on the new injury.
Various alternate takes on this experiment have been previously featured in 755: Interdisciplinary and 1670: Laws of Physics , but this is the first time experiment is performed in a proper manner.
[Cueball holds a bowling ball in both hands. It is attached to a string that goes behind him and up disappearing off panel around double his height. He is talking to Megan, Hairy, and Ponytail who is looking at him. Between Cueball and the other three is a cross in a dotted circle on the floor.] Cueball: If you stand with the bowling ball in front of your face and let go, will you flinch when it swings back?
[Zoom in on Megan in a slim panel. There is a caption in a frame above her.] Caption: Physicist Megan: I won't flinch. Megan: I trust conservation of energy.
[Zoom in on Hairy, in a wide panel. He has lifted arm holding his hand palm up toward Cueball (who is off-panel). There is a caption in a frame above him.] Caption: Biologist Hairy: I trust my flinch reflex, which was honed by millions of years of evolution to protect my delicate face. I'm not messing with it.
[Zoom in on Ponytail in a slim panel. There is a caption in a frame above her.] Caption: Engineer Ponytail: I don't trust that you hung that thing up correctly.


TTSLTSWBD

Explanation:
Cueball is standing at a lectern on a podium , addressing a large crowd. He is describing the program of some event, listing the different topics that will be covered. These appear to be random, but the caption gives the punchline: it is a conference on things that seem like they shouldn't work but do.
By "things that seem like they shouldn't work", it means things that the average person would have some intuitive sense that the function of thing was impossible, and yet ample real-world experience shows that they do, and may become a routine function that people depend upon.  TTSLTSWBD in the title and the banner is the abbreviation for "Things That Seem Like They Shouldn't Work, But Do".
Organ transplantation , where a functioning organ is cut out of one person (possibly a dead one) and put into another person where it will now operate for their benefit.  Given the very complex and delicate nature of living tissue, it's rather surprising that this could work at all.  In reality, it's not a simple process, and a lot of things could go wrong, but modern medicine is advanced enough that organ transplantation is widely accepted and regularly practiced, usually functioning well enough to extend life.
Airships , or dirigibles, are huge , rigid structures which are filled with bags of lighter-than-air gas, which causes the entire structure to float, and could carry both passengers and significant loads. The idea of such a huge vessel traveling, able to both move rapidly and float in place, would be hard to imagine if it didn't exist, yet zeppelins functioned and were a practical mode of transportation for a time. Unlike the other things mentioned, airships are largely obsolete (having lost favor due to safety concerns and surpassed by other technologies). Airships are a recurring theme on xkcd.
Lunch is listed as if it was another topic of the TTSLTSWBD, but it actually just means that after discussing airships, the conference will take a break to eat lunch, as many humans usually do. [ citation needed ] Because lunch is a relatively modern construction, filling a niche that grew after dinner shifted later into the day, it may defy one's intuition. In this sense, a three-meal day may seem like it shouldn't work, but most who observe all three meals on schedule would likely argue that it does.
Mechanical gyroscopes are simple devices consisting of a spinning disc mounted inside three concentric gimbals as a fixture, or more often observed at work as a single spindle in a free-standing external frame that can be held or moved around by hand. The rotational inertia of the spinning disc resists change in orientation, and tends to remain in a single orientation (if free to do so) or else exert counter-intuitive forces (where directly encouraged to change its central axis). The notion that a disc can remain so steady can be counterintuitive even to those who understand the physical principles. This weirdness has been previously referenced in 332: Gyroscopes . An optical gyroscope does not mechanically resist any motion but (relying upon an effect originally exploited in a failed attempt to disprove Special Relativity ) ultimately provides similar feedback about the rotation of the unit into which it is mounted.
Butterflies fly with an unusual fluttering pattern, which works in part due to the notoriously complex principles of fluid dynamics that may look like uncontrolled fluttering but yet somehow allows the creature to land directly on specific flowerheads to feed. This is not as intuitively understandable as the flight of larger creatures such as birds.
The title text refers to rotary hooks on sewing machines, which are a complicated (and complicated looking) mechanism whose purpose is to feed one thread in a loop around a whole spool of another thread, and are apparently counterintuitive enough that the conference feels they need a whole day to cover them.
This concept is referenced in 2115: Plutonium .
The conference that the comic pictures is another example of a thing that seems like it shouldn't work but does. At first glance, Cueball seems to be listing a random, disconnected list of topics that will be covered, which runs counter to the format of most conferences. It initially seems inconceivable that enough people would be interested in all of those separate topics for the conference to make a profit (from attendance fees). However, the audience is packed, demonstrating that this is not the case. This may be because many people enjoy the mind-expanding feeling of having their intuitions shattered.
[Cueball stands behind a lectern on a podium, gesturing with one hand held out, speaking to an audience. A banner hangs on the wall over the crowd with large letters on it. Illegible smaller text is written under these letters.] Cueball: Next we have a session on organ transplants and another on airships. Cueball: Then lunch, then we'll have one on gyroscopes and one on butterflies. Banner: TTSLTSWBD
[Caption below panel:] The first annual conference on Things That Seem Like They Shouldn't Work But Do


Occam

Explanation:
This comic invokes three philosophical topics: Occam's Razor , the Barber Paradox and Murphy's Law .
Occam's Razor is the principle that explanations should not postulate more entities than necessary. It is often phrased as "the simplest explanation is best". The word ' razor ' is intended to evoke the image of shaving off superfluous elements.
The Barber Paradox postulates a town barber who shaves all those, and those only, in the town who don’t shave themselves, and asks whether the barber shaves himself. The paradox is that if he does, then he shouldn’t, and if he doesn’t, then he should. It is an attempt at a concrete, real-world analogue of Russell's Paradox in set theory.
Megan tries to invoke Occam's Razor to create a simpler solution to the paradox. Occam's Razor is named in honor of  philosopher William of Ockham (Ockham being a town in England) and she declares that William shaves the barber. Her proposal is humorous and does not of course resolve the paradox, as the barber is still not shaving himself (so he should shave himself, so he shouldn't shave himself...)
The title text invokes Murphy's Law: the expectation that "anything that can go wrong will go wrong." When you shave with a cut-throat razor , there's multiple things that could go wrong , many of which would cause harm to the person being shaved. Alternatively, invoking Murphy's law makes the principle of Occam's Razor itself, or its use in the comic, "go wrong", possibly rendering the solution invalid.
[Megan is holding a hand palm up towards Cueball as they are walking together.] Megan: The simplest explanation is that Occam shaves the barber.


Daylight Calendar

Explanation:
At the time of this posting, the United States had ended daylight saving time (DST) recently, on November 7, and returned to standard time. Daylight saving time is a practice of setting clocks ahead by 1 hour during warmer months to effectively 'borrow' some of the typically unused early morning light and pass it down to the late evening where more people can make use of it. In the United States, daylight saving time starts on the second Sunday in March and ends on the first Sunday in November.
A result of ending of daylight saving time is the sun setting earlier than people are used to, as people have become acclimatised to the shifted clocks — though it does mean an 'extra' hour of light has returned to the seasonally redarkening mornings. The start of the comic may be the start of a typical comment about how the sun seems to set earlier than usual in November; which it does anyway (north of the equator) but the clock-shift makes it even more obvious.
In this comic, however, Randall turns the normal talk about DST on its head by devising a calendar system where the dates "change" based on 12 hours of daylight. This causes shorter "days" in the summer months, which may get more than 12 hours of daylight in a "solar day" and longer "days" in the winter months which would have fewer hours of daylight in a "solar day". As mentioned in the title text, this change would be very pronounced near the poles, which may only get a few hours of daylight per 24 hours in the winter, but conversely may get 20 or more hours of daylight per 24 hours in the summer. Cueball says that he likes the new calendar system, as it gives him more "time" in the winter to complete work - if Cueball is given "3 days" to complete a task, each of those days could be longer than a typical 24 hours. However, this would be reversed in the summer, as each day would be shorter. Also, if this calendar system was in place, his boss could resolve this problem by just giving him 72 hours to complete his task instead of "3 days".
At temperate latitudes and above, as the calendar goes towards winter (for your hemisphere) the length of daylight per daily cycle shortens. Instead of having "long summer days" (i.e. periods of daylight) and shorter ones in the winter, but still the artificial pressures of a regulated 24-hour cycle to adhere to, the proposal seems to be that the date gets incremented whenever (and only when) twelve hours of daylight have passed.
In the summer, a day-count starting at sunrise could require a late-afternoon switch to 'tomorrow', which would in turn be switched earlier still the next day as it was already partly used up, with possibly two date-changes per astronomical day (early morning and mid-evening, for example). As winter draws on, not enough daylight will pass to guarantee a date-change in any single period. On the day of this comic's release - November 15, 2021 - Massachusetts, where Randall lives, gets ten hours and forty five minutes between civil twilights . It is possible that the last day-mark was late during the previous daylight cycle and the next one won't be until early in the following one.
Depending on how exactly daylight is measured, we may have more "days" in a year than the usual 365, since refraction of light near the horizon means that the sun is visible slightly more than 50% of the year on average. This effect is strongest near the poles, since the sun spends more time near the horizon. In addition, due the Earth's elliptical orbit, more northerly parts of the Earth receive more sunlight than southerly parts. Combined, these effects mean that a year at the north pole is 381 "days", compared to 369 at the Equator.
Exactly how the time is marked is not fully explained. Starting each day-period at 00:00 would be easiest, but could be a psychological step too far. One possibility is to set a nominal 00:00 six hours before a day-change, in line with an 'idealised' twelve-hours-of-daylight day, but disregard hours 'belonging' to a prior daylight period. Then keep the clock running (throughout any intervening nights and into the next daylight as necessary) until the date clicks over and realigns as necessary. Clock times would not reach 23:59 for most of the summer, and could far exceed that in the winter. Megan's clock has reached 26:15, by this sunset, and may well be due to be far into the 30-hours range before more daylight and the moving on to the new date and reset time, if not beyond.
Beyond the arctic (and antarctic) circle, twelve hours of daylight would be accumulated up twice per traditional day, at times, while being effectively on hold for much of the other six months, depending upon actual latitude.
[Danish is looking down at her phone which she holds up in her hand, while Cueball stands next to her]: Danish: Ugh, I hate November. It's 26:15 and the sun is setting again! Danish: 3-day days are the worst. Cueball: I like it. I know it's dark, but it's nice to have the extra time on deadlines.
[Caption below the panel]: In our new calendar system, the date changes after every 12 hours of daylight, regardless of how long that takes.


Never Told Anyone

Explanation:
This comic combines stereotypes about two secrets that one would normally be reluctant to share: dark, personal secrets , and passwords . In the comic, Megan appears to be about to tell Cueball a secret of the former variety, but twists it by instead revealing a one-time code (presumably for the use of two-factor authentication for an online account). This is poking fun at the serious-looking warnings that typically accompany the generation of one-time codes. For example: "DO NOT share this code with anyone. We will NEVER call you to ask for it." While this is still something Megan should normally be reluctant to share, it has much less value to Cueball than a personal secret [ citation needed ] unless his intent was to steal Megan's account - and even then it's probably useless, as these codes become invalid after they're used (hence the term "one-time") or a few minutes after generation. Cueball compounds the humor by reacting with a shocked gasp, as one would be more expected to react to a dark secret.
Users are generally warned never to tell their password to anyone, not even a support representative of the site; real technical support reps shouldn't ever need your password, and anyone with a true configured-in authority should never even find it necessary to know/use it. However, one tactic that hackers use to break into accounts is to claim to be calling from the site and say that they need your password to fix some vague and/or mythical problem with the account. The title text says that Megan trusts Cueball so much that, despite knowing this, she would divulge her password to him even if he tried this approach on her. There is a further irony here, as Megan is focusing on the exception to the rule ("Don't even tell an employee" implies "You shouldn't tell anyone ") as if it was the most important factor.
[Megan and Cueball are holding hands, she has turned her head towards him, while he is still looking at the scenery. They are standing on the edge of a cliff, overlooking a vast stretch of land with water to the right and mountains far off. There are many details with lakes and smaller bodies of water on the land, three larger and three smaller clouds near the horizon and the sun is shining from the top right corner.] Megan: I've never told anyone this before.
[Cueball has turned towards Megan, as they are still holding hands, in an otherwise empty panel.] Megan: I know I shouldn't. Megan: But I feel like I can trust you.
[Megan and Cueball are no longer holding hands as he has taken both his hands up in front of his mouth and a sound escapes him, as shown with small lines coming off his head with the speech line going up from above them.] Megan: My one-time code is 263827. Cueball: *Gasp*


Heart-Stopping Texts

Explanation:
Text messages have become a ubiquitous form of communication in most countries, and have become a basic part of many people's everyday lives.  Conversations over text frequently jump straight to the purpose of the communication, without salutation or prelude.  Some texts, particularly when delivered without context, can carry implications that cause immediate anxiety.
"Out of the blue" is an English expression meaning "to appear in a sudden and unexpected fashion". It's a shortened version of  "sudden as a bolt out of the Blue", referring to a bolt of lightning out of the clear, blue sky.  The implication is that something dramatic (and possibly dangerous) is has occurred without any warning signs, under circumstances where it wouldn't normally be expected.
This comic lists texts that would be worrying to receive with no context, for a variety of reasons. It seems to suggest that sending these is a good way to prank someone; particularly the title text, where deliberately sending an animated loading icon seems like it couldn't be intended for any other purpose. The different messages are explained below.
[Comic heading:] Most heart-stopping texts to receive out of the blue
[A collection of light gray text bubbles in two columns:]
Did you forget what day it is?
I bet you're probably getting bombarded with texts right now, huh?
Did you mean to post that to everyone?
Is this your house? cnn.com/2021/11/19/S...
You didn't click on any weird emails recently, did you?
Can I call?
Wait, do you know Joe Rogan? How does he know your name?
Why are you trending on Twitter?


Bayes' Theorem

Explanation:
For example, if a test has a 100% sensitivity (first line, all those affected receive a positive result) and a 99% specificity (second line, 1% of the unaffected also receive a positive result), the interpretation of a positive test depends on the prevalence of the disease in the population. In the example case, the prevalence is 0.1% (third column), so that when the test result is positive (1% of the tests, left column) the subject is actually unaffected nine time out of ten. Although this would be a very performant test, given the relative prevalences involved it will produce overwhelmingly false positives among all positive results. (But, in this example, all those told they are not in danger — almost a hundred times more individuals than test positive — are correctly notified.)
For this same example, the Bayesian formula gives :
P( Affected | Positive ) = P( Positive | Affected ) * P( Affected ) / P( Positive ) = 100% * 0.1% / 1% = 10% and P( Unaffected | Positive ) = P( Positive | Unaffected ) * P( Unaffected ) / P( Positive ) = 0.9009% * 99.9% / 1% = 90%
In this comic, a teacher is presenting a problem which the students are supposed to use Bayes' theorem to solve. However, the off-panel student knows that they are studying Bayes' theorem, so they use that prior knowledge to guess the usual answer to such problems. The punch line is the caption - The student doesn't need to do the calculation because they're familiar with questions involving Bayes' theorem and how they often present the counterintuitive result to illustrate the importance of prevalence to the calculation.
There is perhaps also a self-referential situation here where the student has updated their prior probabilities a number of times for whether the answer was "Yes" to a question involving Bayes' Theorem. If their method of answering "Yes" to every such question has succeeded every time before then by Bayes' theorem they will have a lot of justification to continue to do until they start getting it wrong. The prevalence of Bayes Theorem questions that require the answer "No" might be small enough that this doesn't happen in any small number of times and so they learn nothing of the false-positive rate until that point in time. This could be interpreted as a criticism of Bayesian Statistics which may treat a judgement as well justified (e.g. getting the question right) despite lacking a clear understanding of mechanism (e.g. basing your answer to the question on the numbers provided).
The title text refers to the mathematical definition of Bayes' theorem: P(A | B) = P(B|A) * P(A) / P(B). Here, P(A|B) represents the probability of some event A occurring, given that B has occurred. This is often referred to as "the probability of A given B". It can be hard to remember if P(A|B) means probability of A given B, or if it's B given A, especially when talking about the probability of an earlier cause given a later effect. Randall's joke is based on this difficulty. Here P((B|A)|(A|B)) is meant to be read as the probability that you write (B|A) given that the correct expression is (A|B), which makes it the probability that you got the order of the notation mixed up.
[Miss Lenhart is pointing with a pointer, held in her right hand, to a white-board with tables, what looks like formulae and lots of other unreadable text. She looks toward her off-panel class, from where a voice replies to her question.] Miss Lenhart: Given these prevalences, is it likely that the test result is a false positive? Off-panel voice: Well, this chapter is on Bayes' Theorem, so yes.
[Caption below the panel]: Sometimes, if you understand Bayes' Theorem well enough, you don't need it.


Fiction vs Nonfiction

Explanation:
Cueball is asking Ponytail and White Hat to classify different Star Wars books and movies as fiction or nonfiction.  (Perhaps he is working at a library or bookstore, or sorting a personal collection.) Star Wars as a whole is a multimedia franchise, which includes films, TV series, novels, etc, but often singularly refers to the original 1977 film later more lengthily titled Star Wars: Episode IV – A New Hope (or, given the fact that the rest of the titles are books, one of several novelizations based on the script). The classifications get more complicated to determine as the conversation progresses while revealing a quite specific obsession with the character of Boba Fett . The complexity may even end up converting lumpers into splitters , a philosophical distinction that another recent comic touched upon.
Nonfiction (also spelled non-fiction) is any document or media content that intends, in good faith, to present only truth and accuracy regarding information, events, or people. In contrast, fiction offers information, events, or characters expected to be partly or largely imaginary, or else leaves open if and how the work refers to reality.
In the end, White Hat suggests that, since Cueball has so many works featuring Boba Fett, it would be more useful to group them together in a new category rather than sorting them into the fiction and nonfiction sections.
[Cueball is talking to Ponytail and White Hat.] Cueball: Star Wars ? Ponytail: Fiction.
[Same setting.] Cueball: The Making of Star Wars ? White Hat: Nonfiction.
[Closeup of Cueball.] Cueball: Star Wars: The Adventures of Boba Fett ? Off-panel voice: Fiction.
[Closeup of Ponytail.] Cueball (off-panel): Star Wars: The Official Guide to Boba Fett's Armor and Weapons ? Ponytail: Nonfiction, technically.
[Cueball has lifted a hand palm up as he talks to Ponytail and White Hat.] Cueball: Boba Fett's Gadgets and How He Got Them ? Ponytail: ...Fiction? Ponytail: It depends.
[Cueball is talking to Ponytail and White Hat. Ponytail has turned towards White Hat and has taken a hand to her chin.] Cueball: Boba Fett: A Life , by historian Doris Kearns Goodwin? Ponytail: Hm. White Hat: Maybe we should just have a Boba Fett section.


Siren

Explanation:
Odysseus is the hero of the Greek epic Odyssey by Homer . This is a poem that relates the journey of Odysseus back home to his homeland from the newly defeated Troy, and how he inadvertently angered Poseidon thus causing the journey to take 10 years.
In the story, now widely translated and adapted for modern audiences, Circe warns Odysseus of the Sirens , who sing beautiful songs that lure sailors towards their shores, just to doom the boats to sink upon the jagged rocks surrounding their islands. In Odysseus's own case, the Sirens even claim to be able to " tell you everything that is going to happen over the whole world "; at this point, Odysseus has been away from home for many years and has no idea if his wife and son remember him, so the temptation to stay and listen (and thus find out if he will be able to return alive) is especially powerful.
This comic reframes the advice as if Odysseus was being told to ignore the incorrect instructions of a GPS-linked routefinder , rather than the Sirens. Errors, omissions or out-of-date information in the databases used by such devices famously have sent drivers down roads they might never have even tried to use (guided by printed maps, road-signs or even past experience) without the alluring voice of the 'infallible' dashboard device leading them through too-narrow lanes, into rivers or even hundreds of miles completely out of their way - perhaps to a destination similarly-named to their intended one. GPSs did not exist during the time the poem was written, [ citation needed ] so this could not be the case here.
A navigation system giving wrong directions can happen, for example, due to outdated or incomplete map data. Sometimes users can file an error report with the provider of the navigation system and hope that they fix the problem in a software update. This is what Circe already did multiple times. However, the error was not fixed, so she has to resort to telling Odysseus to ignore the route.
The title text shows what the route description could have looked like, had Odysseus indeed used a modern navigation system. It includes the start and destination of the route, the estimated duration and warnings about special circumstances of the journey.
Normally, the sea voyage from the City of Troy to Ithaca should take much less than ten years. For Odysseus it took so long because of the many obstacles he had to face, so the navigation system would have some sort of clairvoyance function built in.
"Route crosses an international border" and "Route includes a ferry" are standard warnings included in a route description. The former alludes to the facts that Odysseus's voyage took him to many lands and kingdoms while the latter may allude to the fact that in Book XI of the Odyssey, Odysseus visits Hades, which is traditionally reached by a ferry across the river Styx, piloted by Charon the ferryman.  "Route includes capture by the goddess Calypso " is not normally something that a navigation system would warn about or could know about, [ citation needed ] but this indeed happened to Odysseus in Homer's tale; he was kept on her island Ogygia for seven years.
The weird directions in the title text may be a reference to 461: Google Maps .
[Circe is speaking to Odysseus.] Circe: Remember, Odysseus: Circe: As you pass the rocks you will hear a woman calling out to you, urging you to stray from your path, but plug your ears and hold your course, for her beguiling lies will draw you to a watery grave. Circe: I don't know why they can't just fix it. I keep filing error reports.
[Caption below the panel:] Circe was actually just telling Odysseus to ignore his GPS.