Radio Bart - S3-E13
Audio problem: When Homer talks to Marge about Bart's present, the same footage was taken from 'Saturdays of Thunder,' because you can see that Homer's mouth doesn't move right. (00:02:40)
Radio Bart - S3-E13
Audio problem: Just after Krusty kicks Sideshow Mel into the big birthday cake on his show, he says "Hey kids" but his mouth doesn't move right.
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.
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