Revealing mistake: During the lightsaber duel, Vader throws his at Luke. The catwalk behind Luke explodes, but if you watch in slow-motion there are two explosions: one some inches over where the lightsaber actually hits and one far on the left.
Revealing mistake: In the scene where Han and Chewie sneak up on the two storm troopers on the Endor moon, Han steps on a twig, it snaps, and the trooper turns around and punches him. Watch in slow motion as the punch is released, Han starts falling backwards before the fist hits him.
Factual error: The cockpit for the Falcon is on the right side of the ship. Why, from the inside, does it always look like it's directly in the center of the front of the ship? The visuals outside are not offset like they should be for a cockpit that's not in the middle of the ship.