Continuity mistake: When Lisa is helpfully explaining what a Bar Mitzvah is, Krusty's new puppy loses its red lead. (00:07:30)
Continuity mistake: While Krusty is describing his prostate to the children, the green umbrella vanishes from beside Lisa. (00:07:40)
Audio problem: When Marge says she wants the padding that goes under rugs her lip movements don't match what she's saying. (00:13:25)
Continuity mistake: When Krusty is sacked, his bottle of pop vanishes. (00:13:45)
Continuity mistake: When Homer writes an autograph for Ralph at the restaurant, Lisa is sitting opposite Marge, has yellow liquid in her glass and has red and brown food on her plate. In the next shot, Lisa is opposite Homer, has a blue drink and has white and green food. (00:14:25)
Continuity mistake: When Homer leaves the studio after being cancelled there is no sign next to the door. When Marge walks up to comfort him there is now a 'stage door' sign there. (00:18:35)
Continuity mistake: During the 'whose garter is this?' joke Patty and Selma appear behind the Simpsons. (00:20:10)
Continuity mistake: In the Itchy and Scratchy cartoon 'A Briss Before Dying', Itchy throws Scratchy's eyes out of the window, but after putting the rest of his body through the grinder the eyes are back.
Continuity mistake: The coathanger is too small to reach the medicine cabinet.
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.
'Tis the Fifteenth Season - S15-E7
Continuity mistake: After the family discover the astrolobe, the gift tag disappears from its wrapping. (00:07:25)
'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)
'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)
'Tis the Fifteenth Season - S15-E7
Continuity mistake: After Homer decides that he doesn't want to sleep with Marge, he goes downstairs and watches TV. He moves to a different side of the sofa between shots.
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)
Marge vs. Singles, Seniors, Childless Couples and Teens, and Gays - S15-E8
Continuity mistake: When Homer sneaks into Maggie's room to smash the CD player, there is a yellow box with musical notes painted on it. The notes are different in each shot. (00:02:30)
Marge vs. Singles, Seniors, Childless Couples and Teens, and Gays - S15-E8
Continuity mistake: When Bart asks Ms. Krabapple for detention, the piece of paper on his desk disappears. (00:03:05)
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)
Marge vs. Singles, Seniors, Childless Couples and Teens, and Gays - S15-E8
Continuity mistake: When we see The Town at the meeting, Smithers is sitting in front of Selma. In the next shot, though, Smithers is suddenly on stage holding the 'SSCCATAGAPP' sign and Lenny is sitting in front of Selma. (00:08:50)
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)
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