The City of New York vs. Homer Simpson - S9-E1
Factual error: The windows of the World Trade Center couldn't open and the Twin Towers weren't in front of each other as depicted in this episode. They were at an angle.
The City of New York vs. Homer Simpson - S9-E1
Factual error: The windows of the World Trade Center couldn't open and the Twin Towers weren't in front of each other as depicted in this episode. They were at an angle.
Continuity mistake: When Homer's Vegas wife shows him the video in front of Marge, it shows Homer kissing Ned. This didn't happen when she showed it in the Vegas episode.
Skinner's Sense of Snow - S12-E8
Nelson: Hey, look how much Skinner makes: $25,000 a year.
Bart: Let's see, he's 40 years old times 25 grand. Whoa, he's a millionaire.
Skinner: I wasn't a principal when I was one.
Nelson: Plus, in the summer, he paints houses.
Milhouse: He's a billionaire.
Skinner: If I were a billionaire, why would I be living with my mother? [All the kids laugh at him.] They're just not responding to logic anymore.

Trivia: Maggie scans as $847.63 in the supermarket at the beginning (not NRA4EVER, as Troy Maclure asserts in 3F31 "The Simpsons 138th Episode Spectacular), the price it costs to feed and care for the average American baby every month.
Tree House of Horror V - S6-E6
Question: Homer travels back in time and causes changes by what he does in the past, like stepping on a bug. I once saw a movie with the same basic plot: some people travel back in time and are told to be careful not to disturb anything, but when they return to their time everything has changed. In the end they discover it was because they stepped on a butterfly. Does anyone know the name of this movie?
Answer: I'm not sure if this is the one you're thinking of, but an episode of "Ray Bradbury Theatre," called "A Sound of Thunder," dealt with a similar matter: a group of hunters travel back in time to hunt dinosaurs, only to find things have changed when they get back because someone stepped on a butterfly.
Xofer