Easter egg: On Disc 4, go to the Special Features from the main menu. On this menu, type in 742 (the Simpsons' house number) to view some hidden sketches. (Note: You may have to press Enter between each of the numbers.).
Easter egg: On four episodes, there are secret commentaries. Select one of the following episodes and then select the Special Features menu for that episode. Press '10' at this screen to be taken to a new screen where it offers a hidden second commentary with one of the executive producers. This only works on "Stark Raving Dad" (Disc 1), "Lisa's Pony" (Disc 2), "Separate Vocations" and "Bart the Lover" (both disc 3).
Easter egg: On Disc 3, at the Main Menu, type in 84763 (this is Maggie's cost; see opening credits) and you will automatically be taken to an Audio Outtakes menu. (Number keys are obviously necessary.)
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