500 Keys/References

==Cultural references==
*Lisa thinks of and while trying to figure out a way to get back the school key. Due to the time since the books were originally created, they have all perished except for Nancy, who is dead by the time Lisa gets the key duplicated.
*The scene where Nelson repeats, "And the day before that", while also walking backwards is a reference to the SpongeBob SquarePants episode, The Algae's Always Greener, where Krabs says "And the next day" repeatedly to Plankton. Also, Nelson speaks through the loudspeaker, which is similar to when Krabs speaks to Plankton on the phone.
*The quote by Chief Wiggum when the police blimp crashes, "Oh the Zoo-manity!" is a reference to the Hindenberg disaster. Zoo-manit by Cirque Du Soleil was mentioned by Bart in "Marge's Son Poisoning".
==Trivia==
*Lisa's saxophone is replaced with a violin in the opening sequence.
*It is learned that Maggie can use the keys without help from her family.
*Skinner confirms, once again, that the school is unaccredited.
*The aired version of the chalkboard gag is an apology to Kristen Schaal for misspelling her name in the credits for "Homer Scissorhands".
*In the fake classroom there is symbols for the four elements (Fire, Air, Earth, Water) visible, as depicted in Avatar.
*This is the second episode where Chief Wiggum fails to catch something going between his legs. The first was "Coming to Homerica".
*This is the second episode to show Otto crashing a bus full of children off a bridge and into a water source. Otto previously did so in "Das Bus", but on that occasion, the kids on the bus got stranded on a deserted island.
*When Lisa enters the banned book room for the first time, a hamster corpse in an orange transparent ball can be seen. This is a possible reference to the Deweys' hamster in Malcolm in the Middle. It might also be Nibbles in the ball from the episode "Skinner's Sense of Snow", or Superdude who died in "Who Shot Mr. Burns? (Part One)".
*This is the second time Lisa has found a hidden room inside Springfield Elementary, and when she shows others the room, a false wall was built to hide the hidden room (the first was "Grift of the Magi").
*Homer drives the Duff Blimp in this episode, after previously longing to ride the blimp in "Duffless".
== Continuity ==
* Homer has keys from older episodes including:
** Homer the Smithers - Keys to Burns Manor
** Sex, Pies, and Idiot Scrapes - From his brief stint as a bounty hunter
** Midnight Towboy - Keys to Homer's old tow truck
** Deep Space Homer - Key to NASA shuttle (at airtime, the first space shuttles were being retired)
** Mr. Plow - The keys to Homer's snowplow
== Goofs' ==
* According to this episode, Otto has believed since he crashed a bus years before that he had killed several children. However, in "The Otto Show" he claimed that in all of his fifteen crashes there were no fatalities. This may have simply been a cover-up to keep himself out of trouble.
Category:Trivia
Category:Cultural references
Category:Episode references