Continuity mistake: When Marge says good night to Bart he has pyjamas with sleeves on. Then when he puts on Lisa's nightgown (which doesn't have sleeves) to make Marge think he is Lisa, Bart's pyjama sleeves can't be seen under Lisa's nightgown. (00:12:25)
Continuity mistake: During the 20 years ago flashback, when Maude goes to spray water on Homer's pants, she is sitting on a tree in the background. When Homer and Marge talk, she doesn't spray water on his pants, but in the next shot she is gone. (00:17:35)
The Burns and the Bees - S20-E8
Factual error: When the bees fly to Mr. Burns' stadium, they are shown as seeing the stadium with 11 eyes. Bees only have 5 eyes. (00:18:15)
Revealing mistake: At the craft store when Homer and Bart go in, the door opens before Homer pulls the handle. (00:14:00)
Other mistake: When Homer throws his beer bottle in the air and puts the gun in his mouth, the beer bottle never lands. (00:15:30)
Character mistake: When Maggie starts speaking Ogdenvillian, Marge says that it is her first word. But in the episode "Gump Roast", everyone, the Simpsons included, all watched a video of Maggie saying her first word. (00:17:35)
Homer and Lisa Exchange Cross Words - S20-E6
Plot hole: Gil would have been disqualified for cheating at the Crossword Championship. (00:15:00)
Answer: Willy referred to an encounter he believed he had with actual aliens, while Wiggum thought he was referring to the arcade game.