Revealing mistake: In the scene at the end of the very first battle, where Imperial troops have just taken control of Princess Leia's rebel ship, Darth Vader breaks the neck of the Captain Antilles and tosses his body to the wall. The "dead" Captain puts up both of his hands to avoid slamming his face into the wall. (00:05:40)
Revealing mistake: Near the end of the film, the mayor, played by Jim Backus, is speaking to Elliot the dragon, who is invisible. The mayor has a cigar in his mouth and smashes it when he turns to greet Elliot. The scene is accomplished by having Backus turn and smash the cigar into a large pane of glass. However, the reflections on the glass are visible.