Elementary School Musical - S22-E1
Other mistake: As Stephen Hawking rotates in circles, his front wheels stay locked in a straight position, rather than turning into the turn.
Elementary School Musical - S22-E1
Other mistake: As Lisa and Marge drive out of Brooklyn, they see a mural painted by the two artists. As the camera looks at Lisa, the mural reflection should be reversed, but isn't.
Other mistake: After Lisa has made Bart leave the baseball team, Lisa and the rest of the baseball team are having pepperoni pizza at Luigi's. Lisa is also eating the pepperoni pizza. However, Lisa is a vegetarian, so why would she eat pizza with meat on it?
Other mistake: In the credits, Kristen Schaal is misspelled Kristen Schall. (00:20:40)
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