Continuity mistake: When we first see union flag on fire, the flames are already consuming over the half of its upper edge. Then when we see it reflected in Hugh's eyes, no more than a half of the edge is burning.
Continuity mistake: When Lisa enters the taxi and we see the door being closed, the camera turns into the full view of the taxi in the next shot, and now we see that the door (the one with company logo on it) has changed its shape between shots.
Two Dozen and One Greyhounds - S6-E20
Continuity mistake: There are twenty-six puppies eating from their bowls in the kitchen. As the title suggests, there's meant to be twenty-five.
Two Dozen and One Greyhounds - S6-E20
Continuity mistake: When they are in Mr Burns' laundry room, it is shown that Bart wasn't wearing his socks. However, part way through this scene, Bart is wearing his shoes and socks again without having time to put them on.
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.
Springfield Connection - S6-E23
Continuity mistake: When Marge sees Homer's car parked illegally over 3 handicapped spots you can see a car parked near Homer's that is orange. Later in the scene when Marge starts writing a ticket up for Homer the car next to Homer's is now a dark brown. (00:14:35 - 00:15:05)
Springfield Connection - S6-E23
Continuity mistake: Before Marge sees Homer parking violation, if you look at where he is parked over the first handicapped spot there is a car parked in the first non-handicapped spot. A bit before Marge arrests him there is now a non-handicapped spot between the car and Homer's car. (00:14:35 - 00:15:05)
Springfield Connection - S6-E23
Continuity mistake: When Marge is lying on the sofa reading her book the red lamp behind her is first seen to be fully red.In a following close up shot it has an orange rim on the bottom of the shade.
Springfield Connection - S6-E23
Continuity mistake: When the Simpsons are eating and the family are praising Marge, Homer's plate is first seen to have a small amount of yellow food and a bit of pink food (meat?).In a later shot when Homer steals and uses Marge's pepper spray he has a large pile of yellow food.
Springfield Connection - S6-E23
Continuity mistake: When Homer first spots Snake dealing, you see Marge with a handbag. In the next shot, the handbag has disappeared.
Springfield Connection - S6-E23
Continuity mistake: When Marge is making celery soup, The Front view of her shows just the chopping board in front of her. Then when Lisa talks to her the microwave is seen in front of her.
Springfield Connection - S6-E23
Continuity mistake: When Marge is reading the books on death sports the police arrive and she turns around, you can see the two posts with the round balls on top with no words on it. But when Marge starts walking towards the police station it says "Police" on the balls and the post changes size. Also the door to the police station changes from brown to blue to clear glass and back to blue during the scene.
Springfield Connection - S6-E23
Continuity mistake: When the police pull up outside the station they park three cars in front of the entrance,in front of the steps. In the next shot they are apart on the road, then when Marge walks by them they are in a line to the side of the steps.
Springfield Connection - S6-E23
Continuity mistake: When Hans Moleman and Rev. Lovejoy are in the prison they are sitting to the far right of the bench (which is nearest to Homer's cell). Then in the next shot they are to the far left.
Springfield Connection - S6-E23
Continuity mistake: In the police station the blue light on the ceiling disappears from when the police are seen laughing at Marge.
Springfield Connection - S6-E23
Continuity mistake: When Marge walks into the hair salon, she is carrying a white bag. But in the next shot when she talks to Mrs Krabappel, the bag is gone.
Springfield Connection - S6-E23
Continuity mistake: When Marge is doing her grocery shopping, the boxes of caviar behind her change from green to red.
Springfield Connection - S6-E23
Continuity mistake: When Marge is in the supermarket, she only has about 4 items in the trolley. But just before the trolley crashes into the cheese model, it is full.
Springfield Connection - S6-E23
Continuity mistake: When Marge is shopping, there is a blue baby seat in her trolley. In a following shot of her running with the trolley and it going into the cheese display, the seat has gone.
Springfield Connection - S6-E23
Continuity mistake: When Marge dives under the garage door she leaves a blue estate car. The Simpsons have an orange estate car and a purple saloon, car not a blue estate.
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