Life on the Fast Lane (a.k.a. Jacques to Be Wild) - S1-E9
Continuity mistake: When Homer says "Hold on!" during Marge's birthday dinner, look at his plate and you can see that his fork has been replaced by another knife.
Life on the Fast Lane (a.k.a. Jacques to Be Wild) - S1-E9
Continuity mistake: When we see Homer eating at Marge's birthday dinner at Singing Sirloin, there is a cake on a dish and a wine glass by his plate. When we see Homer a little later on, the cake and wine have disappeared and there is now an ordinary drinking glass by his plate.
Life on the Fast Lane (a.k.a. Jacques to Be Wild) - S1-E9
Continuity mistake: When Homer opens the door with his present, look at the door knocker and you can see that is a completely different one to the one seen at the start of this episode.
Life on the Fast Lane (a.k.a. Jacques to Be Wild) - S1-E9
Continuity mistake: When Lisa asks "What did you get?" when holding the tray, you can see next to her there is a cup, but in the next shot the cup has changed into a glass of milk.
Audio problem: When Lenny introduces Princess Kashmir, his mouth is open without moving when he says "presenting", and when he says "Princess Kashmir", his mouth only moves when he says "Princess", but is closed when he says "Kashmir." (00:07:50)
Audio problem: When princess Kashmere is introduced, we hear Homer laughing, however we see him eating and not opening his mouth. (00:08:00)
Audio problem: During the party, when Princess Kashmir asks Homer to dance, her mouth doesn't move. (00:08:10)
Continuity mistake: Milhouse makes a copy of Bart's photo for a brown skinned boy, but the boy's skin turns yellow when his father scolds him. (00:09:40)
Revealing mistake: When Bart makes a copy of his photo for Lewis, footage of Milhouse inserting a coin into the copy machine is used. You can see Milhouse's pink shirt sleeve instead of Bart's orange shirt sleeve. This same shot is again reused a third time seconds later. (00:09:55)
Continuity mistake: When Marge kicks Homer out he turns away from the door. When she slams the door he is now stood facing it completely. (00:12:40)
Continuity mistake: When Homer and Bart are at the cabaret show, Mr. Burns and Smithers are there with two women. In almost all of the shots there is a woman sitting between Burns and Smithers, except in the close-up of them when Burns asks "How does he DO it?". Then Smithers is shown as sitting right next to Mr. Burns. (00:21:00)
Audio problem: Both Lenny and Carl's voices are wrong. At one point Carl's voice is higher pitched, and Lenny keeps speaking like Moe, or like a voice we haven't heard before.
Continuity mistake: When Bart and his friends are making copies of the photo of Homer, the banner across the copier says "Copies 5 cents," but when they go to deposit the money it says 10 cents.
Other mistake: After Ugolin (one of the French men looking after Bart) has taken Bart to the Chateau Maison, Cesar and Ugolin speak. (they aren't visible in this shot) Ugolin says "Escape is impossible", but the subtitles say that Cesar says it and vice versa for when Cesar actually speaks.
Continuity mistake: When Bart is standing under the shelter of "Bon Dormir", the pavement on which he is standing is grey. But when he is talking to a policeman, the pavement is now a more darker grey.
Continuity mistake: When Cesar and Ugolin are eating their lunch, Ugolin's dish only has some potatoes in it. A few seconds later, the dish now has two sausages added to it.
Continuity mistake: When we see Lisa eating her dinner, she has a glass of water by her plate. But when we see a full view of the table, the glass has gone.
Continuity mistake: When Adil is speaking to Lisa at dinner at the Simpsons' house, Lisa has a knife and spoon by the side of her dish. In the next shot, both items have disappeared.
Continuity mistake: When Bart is sitting in the bike passenger seat on his way to the Chateau Maison in France, you can see the seat is coloured brown, but when he arrives at the Chateau, the seat is now blue.
Continuity mistake: When Homer is saying goodbye to Bart at the airport, there is a metal fence behind him that changes position between shots.
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