Star Wars: Episode V - The Empire Strikes Back (1980)

Revealing: When Captain Needa is killed by Darth Vader because they lost track of the Millennium Falcon, in the background, two guards come to take him away. You can clearly see the dead captain get up almost by himself.

Revealing: When the Falcon leaves Hoth and is being chased by the Empire, there is a scene where the ship gets rocked about. During the 'impact', C-3P0's arm becomes dislodged, and you can clearly see human skin underneath.

Revealing: When the Falcon gets hit by an asteroid, Leia falls and is caught by Han. She tells him that "being held by you isn't quite enough to get me excited". As she is saying this you can clearly see Harrison Ford mouthing her exact words.

The Special Edition covers of Return of the Jedi and Empire Strikes Back are wrong. The picture of the Emperor on ESB cover is from 'ROTJ', and the lightsaber duel between Luke and Vader on the cover of ROTJ is taken from 'ESB' (notice Luke is in his fighter pilot suit, and Vader is fighting him one-handed)

There was a false page in the original script in order to fool all of the people working on the film. This was to keep it secret that Darth Vader was Luke's father. Only George Lucas, the producers and James Earl Jones knew the truth. Mark Hamill was told just moments before filming this scene so his reaction would be right, while David Prowse read the lines from the original script "Obi-Wan killed your father."

Originally, Boba Fett was supposed to be sort of an Imperial Super-Stormtrooper (in their trademark white armor). This idea was - in a way - reused in 'Attack of the Clones', with his father Jango Fett being the genetic father of the Stormtrooper clones.