Continuity mistake: When Bart crashes at the social club, his skateboard changes position between shots. (00:05:30)
Continuity mistake: During the Itchy and Scratchy cartoon, things change about the positions of the cats, the clothing, etc. (00:07:55)
Continuity mistake: When we first see the papers on top of Skinner, the jar of preserves is not visible anywhere. It is beside him in the next shot. (00:19:15)
Continuity mistake: Bart's bruised eye has healed by the time he reaches Skinner's office to lick envelopes. (00:02:40)
Continuity mistake: When the mobsters enter Skinner's office, the phone on his desk changes position between shots. Also, the name bar on his desk doesn't read anything on it. (00:13:50)
Continuity mistake: In the beginning, when Bart finds that the dog ate his homework, the poster on Bart's door has disappeared for one shot. (00:01:45)
Continuity mistake: When the pile of newspapers fall on principal Skinner, two garbage cans appear out of nowhere beside the door. (00:19:10)
Continuity mistake: When Homer is gambling with the gangsters, you can just barely see the shoulder of an ORANGE shirt that Bart is wearing, but in all other shots he is wearing his tuxedo. (00:12:10)
Continuity mistake: Bart's drawing of Principal Skinner is gone when Mrs. Krabappel says that he is missing. (00:14:05)
Continuity mistake: When we see Skinner's car before the newspapers fall on him, it is a light-brownish color. When the police arrive, it is the same color as the cop cars. (00:19:10)
Continuity mistake: When Bart realizes he forgot his permission slip, the camera shows us that the paper is half-under his pillow. However, when he got out of his bed at the very beginning, the paper wasn't under his pillow. (00:01:00 - 00:03:05)
Continuity mistake: When the newspapers fall on Skinner, the rake in the corner has turned into a shovel. (00:19:10)
Continuity mistake: At the beginning, if you watch the clock as Homer walks in, the time changes between shots. (00:01:30)
Continuity mistake: The paper that Bart draws Skinner on changes from ruled to plain. (00:14:00)
Continuity mistake: When the paper falls on Skinner there are blue and white tiles in the doorway, when he is hanging from the hoover, the floor is completely blue. (00:19:20)
Continuity mistake: When Bart draws Skinner before he is declared missing, the paper is flat on the desk in the first shot and held upright in the next. (00:14:05)
Continuity mistake: After Itchy and Scratchy we see Bart and the mob sat in the bar, the mobster at the end of the bar has his drink in 1 hand or 2 hands depending on the shot. (00:08:16)
Continuity mistake: Bart clears some dust off the picture of the Manhattan, once he's made the drink a few seconds later all the dust has gone. (00:06:40)
Continuity mistake: The drink above the Manhattan on the board changes name and picture. (00:06:40)
Continuity mistake: When Bart falls in the entranceway, a puddle appears under his head between shots. (00:05:30)
Answer: Willy referred to an encounter he believed he had with actual aliens, while Wiggum thought he was referring to the arcade game.