Revealing mistake: When Alberto says "If you had completed your seduction of me, I never would have met Sylvia," his shirt collar briefly turns into the same color as his blazer.
Mypods and Boomsticks - S20-E7
Revealing mistake: When Bashir leaves the Simpson house, he doesn't have any eyebrows. (00:12:40)
Revealing mistake: At the craft store when Homer and Bart go in, the door opens before Homer pulls the handle. (00:14:00)
Revealing mistake: While Lou is talking to Chief Wiggum about having his belt stuck to a street sign, Lou's mouth disappears for a single frame.
Answer: Willy referred to an encounter he believed he had with actual aliens, while Wiggum thought he was referring to the arcade game.