Continuity mistake: On the bus, Otto rewinds his tape and there is a shot of the kids. In this shot, we can see the kids and nothing else. A couple of shots later, a food box has appeared out of nowhere.
Revealing mistake: At the U.N. meeting, Bart places his glasses down on the table to read out the Libyan exports. As he puts the glasses down, you can see they are unrealistically floating in the air.
Continuity mistake: At the Model U.N. meeting, Bart finishes speaking and puts down his papers on the right hand side of his desk. Two shots later, the papers are on the middle of the desk. (00:03:10)
Continuity mistake: The pens and pencils in the good butter change between shots when Homer begins his website. (00:04:55)
Continuity mistake: The door to Mrs. Krabappel's classroom has a window, but when Bart fakes being sick then walks out of the class (we see the desks as the door closes), the door's window has vanished, and the doorknob has switched sides as well. Additionally, earlier, when Bart deliberately falls off his chair in class, note that one of the bars on the back of his chair has gone missing. (00:07:35)
Continuity mistake: When Bart fails the test despite having actually studied, we see the two red "X" marks in the center row of the multiple choice questions, but after Mrs. Krabappel passes Bart because he applied practical knowledge, when Homer hangs the test up on the fridge those two "X" marks in the center have vanished.
Revealing mistake: When Moe grabs Ned Flanders' shirt at the bar, Ned's torso is incorrectly drawn over his arms as well as the mug he is holding. (00:10:50)
Orange Is the New Yellow - S27-E22
Other mistake: When Chief Wiggum contacts "Rafe Waggum's" parents on his phone, he dials the number and places the phone to his ear, but the phone displays the menu screen and not the call screen.
Revealing mistake: When Homer is riding Barney like a bull at Moe's, there are duplicates of Sam and Larry (the barflies) in the same shot.
Continuity mistake: The colour of the school changes from yellow when Martin and Bart are talking before the test to grey when Bart has spoken to Otto about being held back. (00:07:00 - 00:11:00)
Continuity mistake: Milhouse makes a copy of Bart's photo for a brown skinned boy, but the boy's skin turns yellow when his father scolds him. (00:09:40)
Continuity mistake: In the title sequence Mr. Largo has a baton in his hand when conducting. This disappears as he stops conducting to throw Lisa out. (00:00:50)
Continuity mistake: At the end, we see Krusty stood next to Mr. Burns. However, as the camera pans over the crowd he has vanished. (00:20:30)
Continuity mistake: Lisa's posture changes at the breakfast table as Bart talks about the school bus. (00:16:10)
Continuity mistake: During the theater scene, the man in the back with the moustache and green jacket watching the Space Mutants movie changes from having yellow skin to brown skin after Bart blows a raspberry. (00:09:30)
Continuity mistake: The position of the street lamp Bart skates into changes between shots. Notice the lines in the pavement. (00:08:20)
Continuity mistake: When the car pulls up by the theatre, you can see it through Bart's window. As the car drives off it's now trees outside his window. (00:08:00)
Continuity mistake: When Marge is telling Homer off about staying in the car she has gloves on. Camera changes to her saying "Move it" and now her glove has disappeared. Her hand also moves from being on the door to pointing. (00:05:00)
The Call of the Simpsons - S1-E7
Continuity mistake: When Homer is driving through the river, in one shot while Marge is talking, Homer's vest and shirt switch colors (from green shirt and grey vest to grey shirt and green vest). (00:07:15)
There's No Disgrace Like Home - S1-E4
Continuity mistake: When Homer walks in on the family eating dinner, Marge has her feet on the second cushion of the sofa. Camera changes and now they are on the third cushion. (00:08:50)
Answer: Willy referred to an encounter he believed he had with actual aliens, while Wiggum thought he was referring to the arcade game.