Bait-and-Switch: What seems to be a thought baloon with Nelson is actually Nelson burning some books.
Book Ends: The episode starts with "Springfield of Tomorrow" and ends with more of that story being shown.
Chekhov's Gun: The long-abandoned subway is mentioned in the "Springfield of Tomorrow" film.
Comically Missing the Point: After squeezing his way in an abandoned subway station, Homer finds a nickel and squeezes himself out. He then pays the fare and enters again.
Getting Crap Past the Radar: At the end of the "Springfield of Tomorrow" film, it's stated couples can freeze their kids for when they need privacy.
Hands-Off Parenting: When Homer and Marge grew tired of Bart manipulating them, they opted for this until they learned of his plan to destroy Springfield with the abandoned subway.
Harmless Freezing: Happens to a boy in "Springfield of Tomorrow" when his parents want privacy.
Idea Bulb: Itchy breaks one and stabs Scratchy with it.
Noodle Incident: Bart was able to cheat on a rectal thermometer. If he doesn’t want to talk about it, then one rather not asks.
Out of Character: Homer is unusually strict in this episode towards Bart. He almost sadistically wants Bart to do more homework than is required of him, and refuses to let him take even a short break despite him actually doing it.
Kid Has a Point: Nelson explains to Bart why he isn’t getting his fix and Lisa at the end.
Something Only They Would Say: Lisa figures out it was Bart who wrote the letter their parents think she wrote because only Bart would misspell "Elementary".