Continuity mistake: When it is announced that Amber is the winner of the contest, and Lisa is runner-up, the stands in the back of the stage are empty. However, when Lisa walks off, all the contestants are back on the stands. (00:15:00)
Continuity mistake: The colour of the alien poster in the nerds' room changes from pink to blue.
Two Dozen and One Greyhounds - S6-E20
Continuity mistake: When they are in Mr Burns' laundry room, it is shown that Bart wasn't wearing his socks. However, part way through this scene, Bart is wearing his shoes and socks again without having time to put them on.
Continuity mistake: When handing out the mail, Marge places a miniature jerry can of petrol on the table. It is gone in the next shot.
Home Away From Homer - S16-E20
Continuity mistake: When Homer tries to leave his seat in the cinema and complains about eating the apple, the shot shows his body fat has wedged him in the seat. However we can see from all the shots before this that the fat was never wedged in like it was when he was trying to leave.
Bart Gets Hit By a Car - S2-E10
Continuity mistake: During Marge's testimony, Lionel Hutz has a neat stack of papers in front of him the whole time. But in the close-up when Homer and Hutz both cover their eyes in sorrow, Hutz has several pieces of crumbled paper and a broken pencil in front of him. The was not nearly enough time for him to make such a mess since the last shot of him.
Homer vs. Patty and Selma - S6-E17
Continuity mistake: At the beginning of the episode, there is a drunk wearing glasses. He disappears in the next shot onwards.
Fat Man and Little Boy - S16-E5
Continuity mistake: When Bart is playing with his toys, we see that in one shot on the shelf there are 4 books, then in the next shot there are 5. (00:03:50)
Continuity mistake: When Bart attempts to skate over Homer's car, his three mates are watching. Between shots they change from standing on the driveway to standing on the pavement. (00:10:55)
Continuity mistake: Wiggum asks Homer for another burger and Homer throws it to him. When he catches it Otto has disappeared from sitting next to Eddie.
Much Apu About Nothing - S7-E23
Continuity mistake: In the final high-up shot of the Simpson's garden with everyone chanting 'No on 24'; Lisa has disappeared from next to Apu, and Ned Flanders' glasses have vanished.
Tree House of Horror II: A Simpsons Halloween - S3-E7
Continuity mistake: After Maggie makes her wish, the family jumps from being in their seats to beside the window. (00:03:50)
Life on the Fast Lane (a.k.a. Jacques to Be Wild) - S1-E9
Continuity mistake: When Marge is on the phone to her sisters, her necklace changes from white to red.
Continuity mistake: At the beginning, when we see the exterior shot of the bus, it is full of kids. In the interior shots, 1) before the twins talk to Bart and Milhouse, every seat is empty, even Sherri and Terri's. 2) when the bus arrives at the school, we AGAIN see a full busload of kids. (00:01:30 - 00:02:25)
Continuity mistake: Marge said to Bart she would make Butterscotch chicken for him, but in the Season 2 episode "Blood Feud" Marge says Bart's allergic to butterscotch.
Continuity mistake: When Homer is sitting in the Frying Dutchman with the crowd gathered round looking at him, the Captain invites people in. Some start walking in, but in the next shot where they are all gathered round again, it is the same group of people again. (00:17:00)
Pygmoelian - S11-E16
Continuity mistake: At the start of the episode, Homer wakes the family up and they get in the car in their night clothes. When they arrive at the destination, they are dressed.
Continuity mistake: After Selma gives Madam Wu the sack of ten thousand "happinesses" the sack instantly vanishes from off the table. (00:08:40)
Tree House of Horror II: A Simpsons Halloween - S3-E7
Continuity mistake: When Jimbo and Kearney take Homer's candy, it is obviously night time. However if you watch the outside as Homer closes the door before he says "Lousy punks" it shows a daytime sky.
Answer: Willy referred to an encounter he believed he had with actual aliens, while Wiggum thought he was referring to the arcade game.