Tree House of Horror II: A Simpsons Halloween - S3-E7
Other mistake: As Kang and Kodos fly away from Earth in their spaceship, you can see that the Earth has been coloured wrong. The continents are blue, and the sea is green.
Oh, Brother, Where Are Thou? - S2-E15
Audio problem: When Homer is praying, he finishes the prayer by saying, "Amen," but his mouth doesn't move when he says it.
Stop Or My Dog Will Shoot - S18-E20
Continuity mistake: In the scene where the dog chases Snake into a playground, Santa's little helper starts pulling the ropes off the top of the climbing frame, in one shot the dog has two ropes left but when we see Snake the dog chews through one rope and the whole thing falls.
Other mistake: When Nelson puts the intestine into the model's mouth, the size of the gut should not increase. It is the same amount of stuff going in a cycle, so where does all the stuff come from? (00:03:15)
Other mistake: The amount of gunk that come from Bart's model at the start is not proportionate to the size of the model. In other words, there couldn't be enough gunk to cover the entire inside of the bus.
Continuity mistake: While Bart is being beaten up by Nelson and Jimbo, Nelson is on the right side and Jimbo is on the left side. In the close up shot, you can see from their arms that Nelson and Jimbo have switched sides.
My Big Fat Geek Wedding - S15-E17
Continuity mistake: When Milhouse is hit by the rock in class, the map behind him changes colors. This actually happens within the same shot between frames.
The Trouble With Trillions - S9-E20
Continuity mistake: In the scene where the FBI agent and Homer are going into the photo booth to view the video, look to the right of the photo booth before they enter. There is a white cup next to the booth. After they have watched the video and are standing outside the booth talking, the cup is now red instead of white.
Continuity mistake: When Bart and Ralph twist the key into the armed switch, the armed sticker is red and the off sticker is yellow. Then, during the press conference, the stickers switch colors. Then, when Mayor Quimby sits in the electric chair, they switch back.
Last Exit to Springfield - S4-E17
Continuity mistake: When the dentist shows Ralph the Big Book of British Smiles, he first shows him a picture of Sherlock Holmes with horrid teeth and all of his teeth are there. When Ralph starts getting terrified of it, it shows the same picture, but this time one of his teeth on the bottom right hand corner of his mouth is missing.
Bart Gets an Elephant - S5-E17
Continuity mistake: Immediately after being chained to a tree, Stampy crushes several objects (a lawnmower, a bike, a doghouse, and a trash can). In the very next shot, which comes after a commercial break, all of these objects are in fine shape. Then the shot changes again and we see them destroyed once again. (00:09:30)
Continuity mistake: When Agnes meets Bart and his friend, it cuts to Skinner, then to Bart's group and quickly back to Skinner. When it goes to Bart's group (before Skinner) Lewis is yellow like the rest, in all other scenes he is black.
Continuity mistake: Just before Lisa's Presidential "refund adjustment" speech she pushes Bart's tape player off the desk and we can hear it smash off screen. Later in the episode when Lisa agrees to legalise it, he starts playing the same player.
Continuity mistake: During The Town hall scene, Ruth Powers (the woman with the red bandana) is seen with blondish hair in two shots. All other shots of her during this scene shows her with her usual brown hair.
Itchy and Scratchy: The Movie - S4-E6
Revealing mistake: When Nelson blinks right before Milhouse says "No one who saw the movie would say that", Nelson's right eyelid is white for some reason. (00:18:20)
Tree House of Horror II: A Simpsons Halloween - S3-E7
Audio problem: When the guy who Homer buys the monkey's paw from tells him that he'll be sorry, his mouth doesn't move. (00:03:10)
Continuity mistake: When the women of the neighbourhood throw Marge a baby shower because she's pregnant with Maggie, Ruth Powers is one of the ladies there. Ruth only met Marge when she moved to Springfield with her daughter in "New Kid on the Block" (Maggie was already born in the episode).
Homer's Triple Bypass - S4-E11
Factual error: I get it, it's a comedy. But after open heart surgery, you are sedated for 1-2 days and on a ventilator. So, Homer even being awake after open heart surgery is completely false. Also, as someone who has had open heart surgery, you can barely move your chest because your sternum is fractured.
Answer: Willy referred to an encounter he believed he had with actual aliens, while Wiggum thought he was referring to the arcade game.