Homer Alone - S3-E15
Audio problem: When Lisa screams "Mom" on the way to school, she just leaves her mouth open and doesn't close it. It should sound like "Maaaaaa" if she keeps her mouth open. (00:03:20)
Homer Alone - S3-E15
Audio problem: When Marge is running errands, Homer gives her his bowling ball with a bottle cap stuck in a hole. She then takes it to Nicks. When he says, "Sorry lady, you've got the wrong Nicks," he shakes his head and makes an "Ohh" shape with his mouth, not saying anything. (00:03:50)
Homer Alone - S3-E15
Audio problem: At the start in the kitchen when Homer, Bart and Lisa are all talking over each other, their mouths don't match what they're saying. (00:02:30)
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