Revealing mistake: When all the students are leaving Springfield Elementary after the fire alarm is pulled, the same students keep passing over and over again.
Revealing mistake: During Skinner's speech to the students in the school cafeteria, two Allison Taylors are seen sitting on different sides of the cafeteria.
Continuity mistake: When Homer arrives at the Van Houten house for Milhouse's party, Janey is among those at the entrance and she appears with yellow skin twice.
Revealing mistake: When everyone is in Ned's shelter, the woman in the top left hand corner with brown hair and brown skin briefly has 2 pupils in each eye.
Grandpa vs. Sexual Inadequacy - S6-E10
Continuity mistake: In one scene in Bart's treehouse, Wendell's skin is yellow, rather than its usual white color.
Continuity mistake: When Chief Wiggum pulls Homer over for speeding, all the clown decorations on his car have disappeared.
Other mistake: When Bart is looking at space through his telescope, Earth can be seen through the telescope despite him being on Earth.
Continuity mistake: When the Shelbyville kids drop the basket of lemons when Bart and friends start throwing lemons at them, the position of the basket changes when the Shelbyville kids run off. Note the colour of the Springfield grass and the Shelbyville grass.
Who Shot Mr. Burns? (1) - S6-E25
Other mistake: In the very first scene, when Principal Skinner is opening the door to the school, there is no name on the school. (00:00:25)
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.
Who Shot Mr. Burns? (1) - S6-E25
Revealing mistake: Right at the beginning, watch as Principle Skinner enters the classroom, there's a clock on the top left hand of the screen. The majority of the left side of the clock is not drawn in.
Tree House of Horror V - S6-E6
Continuity mistake: In "Nightmare Cafeteria", a teacher walks into the classroom and sees Bart sitting at his desk facing backwards. At this point, you can see the lockers behind the teacher are white, but in the next shot they are blue.
Tree House of Horror V - S6-E6
Continuity mistake: In "Nightmare Cafeteria", when Bart is being served his lunch at the lunchroom, his tray is initially plain but in the next shot it is now divided into six squared segments.
Tree House of Horror V - S6-E6
Continuity mistake: In "The Shinning", Homer is eating a bag of crisps while sitting on the sofa and you can see "Potato Crisps" logo on the bag is coloured red, but in the next shot it is now blue.
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.
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?
Answer: Willy referred to an encounter he believed he had with actual aliens, while Wiggum thought he was referring to the arcade game.