Dude, Where's My Ranch? - S14-E18
The Simpsons Family: ♪ Just hear those sleigh bells jingling...
Blue-haired Lawyer: Cease and desist! You are forbidden to perform that song without paying royalties to the copyright owner.
Marge: Nobody owns Christmas carols. They belong to everyone, like grapes at the grocery store.
Blue-haired Lawyer: Not true, but you are welcome to sing the many public domain carols, such as "O Tannenbaum," "Good King Wenceslas," "Jesu, Joy of Man's Desiring."
Homer: Those suck! They're worse than nothing! I could write way better songs.
Blue-haired Lawyer: Go ahead, but don't use A-flat or G-natural, those notes are owned by Disney.
Homer: [Moans.]
Blue-haired Lawyer: That's A-flat.
Homer: [Moans in a higher pitch.]
Blue-haired Lawyer: That's better.
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