Tree House of Horror III: The Simpson's Halloween Special III - S4-E5
Plot hole: At the theatre in the "King Homer" bit, the audience are treated to a traditional showgirl spectacle. But the girls have no curtain behind them, and so the audience should have seen Homer the ape, but they act completely surprised a minute later when Homer comes on. (00:11:40)
Lisa's Sax - S9-E3
Plot hole: In this episode, Homer repeatedly says that they have no air-con or thermostat, but we saw that they had a thermostat in the first clip show episode. What happened to it?
Plot hole: Warren's (as Bob) face falls off and tries to hold it with his hand. When he appears in the next scene, his face is totally sealed with nothing to seal it with. (00:16:25 - 00:17:55)
Simpsons Bible Stories - S10-E18
Plot hole: Somehow, despite being enslaved and being nowhere near anything that could help them, the Jews have a camel, which we did not see coming across the channel.
Homer and Lisa Exchange Cross Words - S20-E6
Plot hole: Gil would have been disqualified for cheating at the Crossword Championship. (00:15:00)
Plot hole: When Bart locks Principal Skinner and Mrs Krabappel in Skinner's office, and tells them that they can't come out until they've reached an agreement, why didn't Skinner and Krabappel just climb out Skinner's office window instead of spending hours pounding on the door yelling to be let out?
Answer: Willy referred to an encounter he believed he had with actual aliens, while Wiggum thought he was referring to the arcade game.