Little Girl in the Big Ten - S13-E20
Continuity mistake: After Lisa's dream she lines up and the girl on the bars is the same girl the teacher told to go out.
Little Girl in the Big Ten - S13-E20
Other mistake: Sherri and Terri are seen participating in the second grade gymnastics (as referred by the gym teacher), even though they're in the fourth grade.
Little Girl in the Big Ten - S13-E20
Revealing mistake: When Bart says "I don't feel so good" after being bitten by a mosquito, his lower body under the table is not visible.
Answer: Willy referred to an encounter he believed he had with actual aliens, while Wiggum thought he was referring to the arcade game.