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.
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