Sweet Seymour Skinner's Baadasssss Song - S5-E19
Continuity mistake: Near the beginning of the episode, Bart is thinking what it would be like to get out of school, you can see his desk quite well and there is nothing on it. But when Bart has finished thinking, a piece of paper has just appeared on his desk.
Sweet Seymour Skinner's Baadasssss Song - S5-E19
Continuity mistake: When Marge, Bart and Lisa are watching the videos at the beginning of the episode, the clock changes from one time to a completely different time between shots.
Sweet Seymour Skinner's Baadasssss Song - S5-E19
Continuity mistake: In the air duct, the dog comes up behind Willie in a straight line and licks his feet, we saw what the duct looked like when Willie turned around. However, when the children start throwing stuff at the duct, from the outside there is a sharp bend right behind where Willie and the dog are that wasn't there in the internal shots.
Answer: Willy referred to an encounter he believed he had with actual aliens, while Wiggum thought he was referring to the arcade game.