Tree House of Horror V - S6-E6
Continuity mistake: In "The Shinning", the family are walking along the corridor at the house with Mr Burns and Smithers and you can see that Homer is walking near a window in one shot, but in the next shot he is now by the railing.
Tree House of Horror V - S6-E6
Continuity mistake: In "The Shinning", on the desk next to the typewriter there is a box of paper and some sheets next to it. But when Marge is on the staircase with a baseball bat, the box and sheets have gone.
Tree House of Horror V - S6-E6
Continuity mistake: In "Time and Punishment", when Homer returns after travelling back in time with the dinosaurs, you can see there is nothing on the desk in front of him, but in the next shot a screwdriver appears from nowhere.
Tree House of Horror V - S6-E6
Continuity mistake: In "Time and Punishment", Homer kills a mosquito whilst back in time with the dinosaurs and you can see in the background there is a volcano, but in the next shot the volcano has gone.
Tree House of Horror V - S6-E6
Continuity mistake: In "Time and Punishment", the family are eating breakfast at the table and you can see there is a glass next to Lisa's plate. But when Lisa says "Dad, your hand is jammed in the toaster!" we cut back to Homer and Lisa and the glass has disappeared.
Tree House of Horror V - S6-E6
Continuity mistake: In "Time and Punishment", Homer has his hand jammed into the toaster and you can see Bart has a plate in front of him at the table. But when we see a view of Bart in the next shot, the plate has gone.
Tree House of Horror V - S6-E6
Continuity mistake: In "Time and Punishment", when Homer is sitting at the breakfast table, he asks Marge to pass a doughnut to him and you can see there is a newspaper next to his plate. But when Homer runs off back to the basement, the newspaper has gone.
Tree House of Horror V - S6-E6
Continuity mistake: In "The Shinning", Homer looks into the mirror and you can see the carpet at the bottom of the steps is coloured pink. But when Homer falls down the steps in the next shot, the carpet is now green.
Tree House of Horror V - S6-E6
Continuity mistake: In "The Shinning", Marge goes to see the typewriter and you can see that viewed from behind the paper in the typewriter is crooked, but when the camera angle changes in the next shot, the paper is now straight.
Tree House of Horror V - S6-E6
Continuity mistake: In "The Shinning", Smithers is helping Mr Burns to put crates of beer into the car and you can see there is nothing on the lid on the car boot, but in the next shot a wheel appears from nowhere.
Continuity mistake: After Homer's emotional outburst about the lack of bananas, when it cuts to the exterior shot of the Lovejoy house the doorknob is on the right side of The Front door, but when Reverend Lovejoy kicks Bart out of his house, the doorknob is on the opposite side. Later, when Jessica twirls the baton, the doorknob is on the right side again. (00:08:00)
Continuity mistake: When Bart is talking to Jessica after she stole the collection plate money, she is far away from Bart. But when Bart says "but you're not very nice", she is right next to him.
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.
Lisa on Ice - S6-E8
Other mistake: As Homer is signing Bart's academic alert form just before Marge starts talking to Lisa you can read the writing below the "Academic Alert" title, but the writing is completely incoherent including sentences such as "IMAEGTSIAD TSNHOJI NAMREB". Update; some of the "words" or parts of them are people's names, such as David, Stuart and Allison, but backwards. (00:03:50)
Lisa on Ice - S6-E8
Revealing mistake: After the buzzer goes on the final game and the crowd reacts one of the crowd members says "Tie Game.", then some woman in a red top says "What the Hell.". If you look at the woman when she moves her head you can see the nose on her face disappears. (00:19:55)
Lisa on Ice - S6-E8
Continuity mistake: When Lisa throws her academic alert into the trash, she jumps half way across the stage without taking a step.
Lisa on Ice - S6-E8
Factual error: The clock in a hockey game does not run during a penalty shot.
Lisa on Ice - S6-E8
Continuity mistake: The turtle that Homer hands to Bart disappears as soon as it goes into Barts' hand, and it is never seen again.
Lisa on Ice - S6-E8
Revealing mistake: While Bart and Lisa are skating off the ice rink, the skin color of one of the people in the background during the riot keeps flashing yellow and brown.
Homer Badman - S6-E9
Revealing mistake: In the scene where Marge's coat pocket bursts open, the candy flows onto the floor. However if you look to the right of her some of the candy seems to almost float above the floor. The candy's direction is completely to the right but because of the floor being angled it spreads over one woman who is standing and there is nothing there to support the candy. (00:04:30)
Answer: I'm not sure if this is the one you're thinking of, but an episode of "Ray Bradbury Theatre," called "A Sound of Thunder," dealt with a similar matter: a group of hunters travel back in time to hunt dinosaurs, only to find things have changed when they get back because someone stepped on a butterfly.
Xofer