Continuity mistake: When Homer says he's going to the cinema, we see his drinking bird working in front of the computer. It makes a key press on the lower right of the keyboard, however on the following close up shot of the bird pressing the Y key it is a standard qwerty keyboard layout.
Continuity mistake: The canister the hippies use to destroy the germs in Burns lab has the words "antibiotics" appear after the clock rings.
Continuity mistake: When Marge talks to cable guy, the trees and hammock disappear.
Continuity mistake: The moss on Walt Whitman's grave when Homer removes it changes.
Continuity mistake: The antenna from Homer's car disappears when he drops Mother Simpson at the gas station.
Sideshow Bob's Last Gleaming - S7-E9
Continuity mistake: When Maggie (sitting on Marge) appears on "Tyrano-Vision," Homer waves his hand in front of her. However, we can see that he isn't leaning over too far, and in the next shot it is clear that both Bart and Lisa are sitting between Homer and Marge, so there is no way he could have reached over to her in the first place.
Sideshow Bob's Last Gleaming - S7-E9
Continuity mistake: When Bart and Lisa first enter the Duff Blimp, Bart doesn't have his back-pack on. However, he is suddenly wearing it after the bomb has gone off.
Sideshow Bob's Last Gleaming - S7-E9
Character mistake: Homer drinks 6 non-alcohol Duff at the air show, but is charged for 8.
Sideshow Bob's Last Gleaming - S7-E9
Factual error: Sideshow Bob couldn't hide out in the Duff blimp's helium pocket because there wouldn't be any oxygen.
Sideshow Bob's Last Gleaming - S7-E9
Continuity mistake: When Homer drives under the plane to save Bart from Sideshow Bob, you can see he drives under the plane twice.
The Simpson's 138th Show Spectacular - S7-E10
Continuity mistake: During the false ending to "Who Shot Mr. Burns: Part 2", Smithers moves position when Burns explains what happened.
Continuity mistake: When Brodka brings Bart to the security office and plays the shoplifters video tape, Troy McClure's trench coat buttons are on his right side (viewer's left), but when Brodka turns off the video the buttons are on Troy's left side, between shots. (00:07:30)
Continuity mistake: After Brodka lets Bart go with a warning the boy rides his bicycle home, and in the closeup the handlebar's single brake lever is at Bart's right hand, but in the next wide shot the brake lever is at his left hand. In the closeup there's also a bar at the center of the handlebar, but it's gone in the wide shot. (00:09:05)
Continuity mistake: At bedtime, while we hear Marge singing to Lisa in her bedroom Bart is lying in his bed, and on Bart's nightstand beside the door there's a framed photo of Krusty and an alarm clock, but in the next closeup the photo has vanished and instead there's a Krusty telephone. (00:15:55)
Continuity mistake: When Marge runs after Bart because he's hiding something under his jacket, Homer pulls out a gate to block Bart's entrance to the TV room. Three different gate styles are shown. (00:20:35)
Continuity mistake: As Bart is forced to show Marge the item (picture frame) he is hiding, he pulls it out of his jacket and he hands it to Marge. As he pulls it out you can see there is nothing in the frame or on the border of the picture frame. After Marge's reaction to the photo we see a close up of the frame and there is now a picture in the frame and some colorful decorations around the frame. Whilst the frame could have been the backside when he pulled it out he never turned it over when handing it to her, and Marge never turned it around when looking at it.
Team Homer - S7-E12
Continuity mistake: During the classroom scene where Bart reveals his Mad magazine shirt, he removes his sweater and puts it on his desk. In the next shot the sweater disappears. (00:03:40)
Team Homer - S7-E12
Continuity mistake: When Moe says Mr. Burns is going to have an accident, he's wearing his pin pals shirt. When Moe hits Mr. Burns, he wears a mask and different clothes. Moments later, when talking to his bowling team again, he's back in his pin pals shirt.
Team Homer - S7-E12
Revealing mistake: When the children are running down the hallway, the animation keeps repeating. Duplicates of the same children are running several times.
Continuity mistake: Just before Marge tries to sell Skinner the tie rack, she is writing on something. She then puts her hands down by her waist, and then brings one up to turn it on and both up to pull the motor out. The point is that the pencil and the item she had in her hands have simply vanished, and we never saw her put them down either.
Answer: Willy referred to an encounter he believed he had with actual aliens, while Wiggum thought he was referring to the arcade game.