Audio problem: At the theatre, when the cook talks to Mark Hamill off-stage he sounds exactly like Moe the bartender.
Audio problem: At the end, where Homer is carrying Mark Hamill out of the theater and Mark says, "Shoot, I forgot my Light saber", his mouth doesn't match what he says, and it keeps moving when he's quiet.
Other mistake: After Bart complains that Jonathan Harris isn't Dr. Smith, Harris says for Bart to meet him in the food court. Then the Robot says "Danger Bart Simpson, danger." How did he know Bart's name?
Audio problem: At the end where Homer is carrying Mark Hamill out of the theatre, Mark's lips don't match with what he's saying.
Revealing mistake: When Fat Tony says,"I am not so much disappointed as I am blinded with rage", the dark circles under his eyes disappear for a split second.
Continuity mistake: A huge fight begins in front of Mark Hamill's stage. Homer, Quimby, Hamill, Bart and Lisa escape the fight through an emergency exit right behind the people fighting. But in a shot of the five running out, the people fighting inside have disappeared.
Answer: Willy referred to an encounter he believed he had with actual aliens, while Wiggum thought he was referring to the arcade game.