Audio problem: When Lisa visits Homer at the plant, they are playing astronauts with the radiation suits. When they spin around and around, Homer is laughing but his mouth stays the same.
Audio problem: When the car drives into the cornfield, Martin is heard screaming, even though he is still asleep.
Continuity mistake: After the boy's car gets crushed, Bart sells Milhouse's glasses for $600. Then Milhouse knocks over the Coke bottles and the clerk gets the money back and keeps the glasses. The next scene, where they try to get on a train that goes to Springfield, you can see Milhouse in his glasses and throughout the rest of the episode.
Answer: Willy referred to an encounter he believed he had with actual aliens, while Wiggum thought he was referring to the arcade game.