My Mother the Carjacker - S15-E2
Other mistake: In the scene where the prisoners are singing along with Mona, two inmates have the same Identity number.
I, (Annoyed Grunt)-bot - S15-E9
Other mistake: When the bullies are riding around Bart and Milhouse there are problems with their water bottles. In some frames they vanish, in some others the bullies' far legs are drawn in front of the bottle. (00:01:40)
Answer: Willy referred to an encounter he believed he had with actual aliens, while Wiggum thought he was referring to the arcade game.