Tree House of Horror X - S11-E4
[The Simpsons are driving down a road as fast as possible.]
Homer: Dear God, it's Homer. If you really love me you'll save my life now.
[The gas needle immediately drops to empty and the car stops.]
Homer: D'oh.
Tree House of Horror X - S11-E4
Professor Frink: In episode BF12, you were battling barbarians while riding a winged Appaloosa. but in the very next scene, my dear, you're clearly atop a winged Arabian. Please to explain it.
Lucy Lawless: Ah, yeah, well, whenever you notice something like that, a wizard did it.
Professor Frink: I see, all right, yes, but in episode AG4...
Lucy Lawless: Wizard!
Professor Frink: Ah, for glavin' out loud!
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