Continuity mistake: During the 'Nightmare on Evergreen Terrace' segment, when Bart is running from Willie, he plans to sink Willie in the sandbox. In the first view of the sandbox it is isolated on a field, yet when Willie is sinking in the sand there is a jungle-gym beside the sandbox.
Continuity mistake: At the garbage man debate, when Homer says 'Then you should have been early.', we see a shot of Lenny laughing. To the right of him, there is an old woman. In the next shot of Chief Wiggum, the same old woman is sitting to the right of him. In the later shot of Wiggum, Miss Hoover is sitting to the right of him and the old woman has disappeared.
Factual error: During the video screening at the Teacher of the Year committee, the panel is watching the teacher who acts like Robin Williams. In the video the main judge says "Next" and pushes a button on the video control. It goes to the video that Bart Simpson sent in. How was this possible? The video control would only fast forward the video and two separate entries would not be sent in on the same tape. The committee wouldn't have spliced the footage together onto the same tape as the tapes were piled up on the desk. At the start of the scene one of the judges mentions to put in the next tape.
Continuity mistake: In "I Know What You Diddly-Iddly Did", there are a few errors: Homer says, "Guess I forgot to put the fog lights in" at a slightly higher pitch to when we heard him say it earlier (When the event actually happened). When Marge actually ran over Ned she did not carry on driving. The flashback shows that Ned was run over without glasses. However in the actual event he had glasses on.
Continuity mistake: At the end of 'Hex and the City,' there is a shot of the wedding cake, then it pans across the people at the wedding, and you can see Homer with his white shirt on. But then when it goes to a closeup, he suddenly has a blue suit and tie on.
Continuity mistake: When the Hamster rolls through the glass of Flanders car it breaks it near the bottom middle of the front windshield. Later on when Flanders and Homer are taking the kids home you can see the break in the glass has now moved to about halfway up the front windshield. On of the following shots it moves back to its original position and then moves back to being around the middle of the windshield.
Deliberate mistake: The mouth on the panda costume is in a constant smile and at no point does Homer change it, even when he is in pain. However, when he is being pulled back under the curtain the mouth is open and the mask has a frightened expression. I suppose this was done on purpose, but it's still a continuity error of sorts.
Add timeDavid Mercier
Other mistake: After the scene where Mr. Burns gives Smithers his picture of him and Elvis Presley, Homer asks Lisa a couple of questions about Germany. At the beginning of this brief scene, Lisa is reading a book, and from her point of view, her eyes are moving from right to left, which shows she is reading the wrong way on a single page.