Revealing mistake: When Luke is being fed to the Rancor, in Jabba the Hutt's dungeon, there are black outlines around the beast's legs, from the composite's blue screen special effect. This was edited out in the special edition rerelease.

Star Wars: Episode VI - Return of the Jedi (1983)
Plot summary
Directed by: Richard Marquand
Starring: Harrison Ford, Frank Oz, James Earl Jones, Mark Hamill, Alec Guinness, Carrie Fisher, Anthony Daniels, Billy Dee Williams, Ian McDiarmid, Kenny Baker, Peter Mayhew, David Prowse
Genres: Action, Adventure, Fantasy, Sci-fi, Star Wars, Thriller
On Tatooine R2D2 and C3P0 approach Jabba the Hut’s palace. R2 bears a holographic message from Luke Skywalker who wants to bargain for the captive Han Solo. To C3P0’s dismay, the droids are presented to Jabba as gifts. Jabba won’t relinquish his favorite wall decoration—Han frozen in carbonite.
A bounty hunter delivers the mighty Chewbacca to Jabba. Now both Han and Chewbacca are his prisoners. That night, the bounty hunter slips into Jabba’s chamber and frees Han from the carbonite. Revived but temporarily blind, he asks who is there. The bounty hunter removes a head mask and speaks—it is Leia. Their reunion is short-lived; Jabba and his wretched retinue discover them. Han is imprisoned and Leia enslaved (wearing the famous gold bikini).
A lone robed figure arrives at Jabba’s palace. Jedi Knight Luke Skywalker has come to negotiate for his friends. When Jabba refuses to barter, Luke demands their release. Jabba drops him into a pit with a rancor beast. Luke kills the rancor, infuriating Jabba. Luke, Han, and Chewbacca are to be executed in the Pit of Sarlaak, a deadly creature burrowed in the desert sand. Meanwhile, Lando Calrissian has secretly infiltrated Jabba’s palace and is disguised as a guard onboard Jabba’s sail barge. Also aboard are C3P0 and R2, who has Luke’s light saber hidden inside.
With Leia chained at his side, Jabba views the proceedings from his barge. Luke, Han and Chewbacca are about to be dropped from the prisoner hovercraft into the pit. Luke issues Jabba a final ultimatum: release them or die. Jabba laughingly refuses. Luke leaps off the plank as R2 ejects his light saber into the air. Luke catches it and attacks and kills the guards. Leia strangles Jabba with the chain. Han, whose eyesight has returned, saves Lando from falling into the pit. Grabbing Leia, Luke swings swashbuckler-style to the hovercraft. They pick up R2 and C3PO and speed off as the barge explodes.
Luke returns to Dagobah to complete his Jedi training while the others head for a rebel base. Luke finds Master Yoda weak and ill. He tells Luke he has nothing more to learn, but he must confront Vader before he is a true Jedi. His final words reveal there is another Skywalker but dies and vanishes without giving further details. Obi Wan appears and tells Luke the other Skywalker is Leia, Luke’s twin sister. Luke rejoins the rebel fleet, but does not yet tell Leia what he knows. Rebel spies have uncovered a new and more powerful Death Star being constructed above Endor. The Alliance plans an attack, but a shield generator on the planet’s surface protects it. Lando will lead the attack group, while Han heads a mission to deactivate the shield generator. Luke, Leia, and Chewbacca volunteer to go with him.
Trivia: When they were filming the scenes on Endor, Peter Mayhew was told to stay close to the set so no one would mistake him for Big Foot and attempt to shoot him.
Question: How come this movie barely showed anything about Luke and Leia's mother? Luke doesn't even ask anyone what her name was (maybe that was hidden from Leia, but he can probably guess that Yoda or Obi-wan would know). I know we can assume that she was discussed off-screen, but they could have revealed a little more about her.
Answer: The Jedi are shown to have something of a blind spot in regards to matters of the heart. Note that when Luke confronts Obi-Wan over lying to him about his father's fate, Obi-Wan's response is haughty and defensive, and gives Luke nothing in terms of regret or apology. They're focused on their mission, not on how Luke feels. Why waste time, in their eyes, telling Luke about his mother? If they had their way, he wouldn't even know about his father. The prequels would make this more explicit, showing that the Jedi are conditioned from the beginning to let go of all "passions" because they could so easily be corrupted, and their inability to understand Anakin's emotions just contributes to his downfall.
Answer: Why can we assume that she was discussed off-screen? Luke's got more important things to talk about than who his mother was. Yoda dies shortly afterwards and Luke's understandably more interested in how Darth Vader, given that he's got to go up against him, can be his father when talking to Obi-wan's ghost shortly after. Not a lot of time for general chit-chat. Behind the scenes, at that point, very little would have been decided about their mother, as it would be irrelevant to the plot of the trilogy and to discuss her on-screen would have wasted time and slowed everything down.





Suggested correction: This was not a "mistake". The outlines showing around the beast's leg were due to the limited CGI technology at the time the film was made. With advances in special effects in the following decades, the filmmakers were able to enhance the CGI quality in later releases.
raywest ★
But it is a mistake to show that the Rancor is not real, and the outlines show that. It's certainly not intentional.
lionhead
Not sure what you mean that the rancor is not real. Of course it's not real. The issue is, at that time, it was not technically possible to show the beastie without the lines showing. I classify a mistake as something that was not intentional. In this case, it was, due to the limitations of CGI in the 1980s.
raywest ★