Other mistake: When somebody throws a cola can at Homer, the can never hits the ground.
The Lastest Gun in the West - S13-E12
Continuity mistake: At the start of the episode, the dog eats Bart's clothes through the letterbox, but a minute later, when the dog next comes to the house and Homer opens the door, there is no letterbox.
The Day the Earth Stood Cool - S24-E7
Audio problem: When Homer says "Can I man hug you?", he mouths "Can I brother hug you?"
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.
Hunka Hunka Burns in Love - S13-E4
Audio problem: When Marge says "New underpants?", she is mouthing "New boxers?"
Audio problem: When Lisa says "Oh no, somebody took my bike", she is mouthing something else.
Revealing mistake: There are two Ruth Powers in the same shot, when the people are crowding on Homer at the mall.
Wild Barts Can't Be Broken - S10-E11
Continuity mistake: Dr. Hibbert's clothes keep changing during the song near the end. He goes from having his white lab coat, a blue sweater, then a pink sweater.
The City of New York vs. Homer Simpson - S9-E1
Continuity mistake: During Homer's flashback, Homer passes the sign that says "Jeremiah's Johnson" twice.
Brother From Another Series - S8-E16
Continuity mistake: Ruth Powers' hair is red in one of the shots of the protesters. Her hair is brown in other shots of her.
Continuity mistake: After Marge bites the candle down to a smaller size, the candle turns back to its original size for a frame.
Continuity mistake: In the shot before Nelson says "Hey, Simpson. Race you", Ralph is seen sitting on the row in front of Martin. But when Ralph says "Go, banana" he is suddenly sitting two rows in front of Martin. (00:05:25)
Character mistake: When Maggie starts speaking Ogdenvillian, Marge says that it is her first word. But in the episode "Gump Roast", everyone, the Simpsons included, all watched a video of Maggie saying her first word. (00:17:35)
Other mistake: When Bart is looking at Doctor Hibbert on the rowing machine, all the pictures on the walls behind him don't have faces on them.
Another Simpson Clip Show - S6-E3
Character mistake: In the first scene, Marge says that it is 9:30pm, but after Homer's flashback, the clock next to Homer reads 11:50.
Homer and Lisa Exchange Cross Words - S20-E6
Plot hole: Gil would have been disqualified for cheating at the Crossword Championship. (00:15:00)
Plot hole: When Bart locks Principal Skinner and Mrs Krabappel in Skinner's office, and tells them that they can't come out until they've reached an agreement, why didn't Skinner and Krabappel just climb out Skinner's office window instead of spending hours pounding on the door yelling to be let out?
Please Homer, Don't Hammer 'Em - S18-E3
Continuity mistake: In this episode Principal Skinner breaks into Bart's doctors office to find out if Bart has a 'kryptonite'. Bart discovered Skinner was allergic to peanuts. On Bart's medical history form under 'known allergies' it has shrimp ticked (they later battle with shrimp and peanut on a stick). However in a previous episode (The Heartbroke Kid, season 16 episode 17) it was discovered that he was allergic to cauliflower, so that should have been on the list as well.
Don't Fear The Roofer - S16-E16
Revealing mistake: When Homer sits on Lenny's cake in Moe's bar, some of the frosting appears to stay in mid air, and when the frosting is on the wall, it doesn't slide to the ground like frosting would.
Continuity mistake: Millhouse's hair color changes from when we first see him to when Bart comes back to the school yard.
Answer: Willy referred to an encounter he believed he had with actual aliens, while Wiggum thought he was referring to the arcade game.