Continuity mistake: When Homer is shouting at Skinner about losing Bart, if you look closely you can see that the box with the red cap goes past Homer. However, when he turns round and sees that red cap on a box, that box has already gone by.
Revealing mistake: When we see people digging Bobo out of the ice, they put him in a bag. If you look carefully you can see another Bobo put in another bag just before the shot changes.
Audio problem: When Homer is talking to the family about their complaints about the nerds, he says something that ends in "where we can all live in harmony". When he says this the audio does not match his mouth movements.
The Last Temptation of Homer - S5-E9
Continuity mistake: When Bart has had his throat sprayed, we see him standing up just before the shot changes to the power plant. The shine on his shoes instantly disappears and reappears several times.
Continuity mistake: When Marge and Ruth and shooting cans, there are five on the fence, then, in the next shot, there are only four.
Secrets of a Successful Marriage - S5-E22
Continuity mistake: When Marge is shopping at the Kwik-E-Mart she puts a red can and a blue can on the counter.When Apu tells her about the offer on hair dye he puts two blue cans into the paper bag.
Deliberate mistake: When Homer pushes the trampoline off the cliff, there is no rock below the falling trampoline. However, in the shot at the bottom a tall rock is visible which was drawn there on purpose for the trampoline to bounce off of, despite not being visible in the first shot.
Continuity mistake: When Homer and Marge are on stage with Brad Goodman, Homer is eating toffee apples. He keeps eating them but they stay the same size.
The Last Temptation of Homer - S5-E9
Revealing mistake: Just before Homer drives backwards into the trout hatchery, when Homer turns the key it is obvious that it is repeated footage of Marge turning the key because the hand is a lot thinner.
Lisa vs. Malibu Stacy - S5-E14
Continuity mistake: During both conversations Lisa has with the real Stacy (the creator of Malibu Stacy), her drink magically refills itself a number of times.
The Boy Who Knew Too Much - S5-E20
Factual error: Apu (an immigrant from India) could not have been selected for the jury because he is not an American citizen, and this was before he became a naturalized citizen in "Much Apu About Nothing".
Burns' Heir - S5-E18
Continuity mistake: Hans Moleman has brown skin at the beginning of the episode and yellow skin at the end.
The Boy Who Knew Too Much - S5-E20
Continuity mistake: During the trial, when Freddy Quimby's lawyer is asking him to come to The Front, the flag to the right of the judge disappears during one shot. (00:13:40)
Burns' Heir - S5-E18
Continuity mistake: A criss-cross pattern appears on the fireplace during the closeup on Smithers after Mr. Burns told him that he doesn't have a heir.
The Boy Who Knew Too Much - S5-E20
Continuity mistake: The American flag at the judge's right transforms to a plain white flag during the trial. (00:12:50 - 00:13:25)
Tree House of Horror IV: The Simpson's Halloween Special IV - S5-E5
Continuity mistake: In "Terror at 5 1/2 Feet", when Milhouse decides that he is going to sit next to Uter, Uter all of sudden moves to the other side of the seat between shots.
Tree House of Horror IV: The Simpson's Halloween Special IV - S5-E5
Continuity mistake: At the end just before the Simpsons say "Happy Halloween everybody" they are about to bite Lisa (and make her a vampire). Maggie has no dummy (or in America, pacifier) in her mouth, but it suddenly appears when she closes her mouth.
$pringfield (or How I Learned to Stop Worrying and Love Legalized Gambling) - S5-E10
Continuity mistake: As Marge arrives home and sees the bullet holes in the door, the shot changes to a POV shot from behind the door and you can see there are some changes in the holes. The first change is there are three bullet holes on the right hand side which are all the same distance from each other, when she enters the middle hole has moved closer to the bottom one. The other change is the large hole in the middle of the door. On the bottom right hand side its shape goes from being a little irregular to a more round shape. (00:16:20)
Sweet Seymour Skinner's Baadasssss Song - S5-E19
Continuity mistake: Near the beginning of the episode, Bart is thinking what it would be like to get out of school, you can see his desk quite well and there is nothing on it. But when Bart has finished thinking, a piece of paper has just appeared on his desk.
Plot hole: In the car chase, Chief Wiggum says that one of the suspects (Marge) "is wearing a green dress, pearls, and a lot of blue hair." However when we see Marge from the police car all we can see is her hair, so how would he have known about the pearls and dress?
Answer: Willy referred to an encounter he believed he had with actual aliens, while Wiggum thought he was referring to the arcade game.