I, (Annoyed Grunt)-bot - S15-E9
Continuity mistake: When Snowball III drowns, the number of weeds and rocks in the fishtank changes between shots. (00:09:15)
'Tis the Fifteenth Season - S15-E7
Continuity mistake: When we first see the skating rink, it has Jasper, Disco Stu, Otto, Apu and Manjua, Sideshow Mel, a couple of children and two couples skating on it. In the next shot we see the Comic Store Guy split his trousers - he wasn't there before. (00:14:00)
Continuity mistake: In the scene where the Simpsons are sitting down to eat dinner, we see Bart pour tomato ketchup all over his potatoes. Then when the shot changes, we can see all the ketchup bottle and the corn has disappeared, and the ketchup has come off his plate. (00:04:50)
Diatribe of a Mad Housewife - S15-E10
Continuity mistake: When Homer comes home in the Ambulance we can see there is a yellow logo on the back passenger door. In one shot it randomly disappears. (00:05:40)
I, (Annoyed Grunt)-bot - S15-E9
Continuity mistake: In this episode it is shown that Snowball I is buried in their backyard, but in other episodes, notable the one where Sideshow Bob becomes mayor, it is established that she is buried in a pet cemetary.
I, (Annoyed Grunt)-bot - S15-E9
Continuity mistake: The cats' graves change position. When Snowball II is buried, they're away from the the tree and near the fence. When Snowball III is buried, the graves are away from the fence and Snowball is among the roots of the tree. (00:04:10 - 00:09:25)
'Tis the Fifteenth Season - S15-E7
Continuity mistake: Homer looks out of his bedroom window at the skating rink he has built in his back garden. Homer and Marge's bedroom is usually at The Front of the house. (00:13:50)
Diatribe of a Mad Housewife - S15-E10
Plot hole: When Marge is looking for inspiration for her novel, she looks at the boat painting in the TV room. On the frame, she reads it and says: "Scene from Moby Dick". Yet in "The Trouble With Trillions", Marge said that she painted it herself for Homer. So then why would she have to read the label to find out where it's from if she painted it?
Continuity mistake: When we first see the medicine cabinet in the Simpson's bathroom the hinges are on the left. When Homer pokes it with the wire it opens as if the hinges are on the other side. The last time we see it, when Lisa rescues Maggie, the door is missing altogether. (00:01:25)
Margical History Tour - S15-E11
Factual error: On the castle where King Henry VIII is supposed to live, the flags at the top have the pattern of the English flag, being a + shaped cross on a coloured background, but it should be a red cross on a white background. Instead it's a white cross on a blue background. Those are the colours of the Scottish flag, but England and Scotland were separate countries at that point in history. And the cross on the Scottish flag is an X shape rather than a + shape anyway.
Continuity mistake: After Lisa unlocks the bathroom door with the coat hanger, the puddle of "baby blood" (Pepto-Bismol) at her feet disappears in the next shot.
Marge vs. Singles, Seniors, Childless Couples and Teens, and Gays - S15-E8
Continuity mistake: When Roofi is singing at the concert, the Roofi head on the curtain is facing the left. Later, it is facing the right.
Catch 'em If You Can - S15-E18
Continuity mistake: When Lisa says "It's called Wicca, and it's empowering" to Bart, her necklace is red instead of white.
Marge vs. Singles, Seniors, Childless Couples and Teens, and Gays - S15-E8
Audio problem: When Marge says "Save our families" at the beginning of her petition, her mouth doesn't move. (00:14:40)
Marge vs. Singles, Seniors, Childless Couples and Teens, and Gays - S15-E8
Continuity mistake: In the bathroom, Lisa can't stand the Roofi CD being played so she pulls the plug out of the plug socket to stop the radio playing. In the next shot, the plug has disappeared from the radio. (00:02:15)
Diatribe of a Mad Housewife - S15-E10
Continuity mistake: When Homer goes to Ned to make sure Marge imagines nothing again, Homer puts his hand through the door, then he puts his hand through the mailbox, then Nelson puts his hand out to steal the doormat. Nelson puts his hand just over the mailbox, then in the next shot when it reveals Nelson is there, his hand is suddenly under the mailbox without enough time to move it.
My Big Fat Geek Wedding - S15-E17
Continuity mistake: When Milhouse is hit by the rock in class, the map behind him changes colors. This actually happens within the same shot between frames.
Marge vs. Singles, Seniors, Childless Couples and Teens, and Gays - S15-E8
Factual error: The symbols on the heads of the Teletubbies on stage are wrong. They did use the word 'teletubbies', so they're meant to be the same as the real world. (00:05:40)
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