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.
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.
But it is a mistake to show that the Rancor is not real, and the outlines show that. It's certainly not intentional.
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.
Revealing mistake: In the early part of the film, Beverly D'Angelo and Chevy Chase check into the hotel/motel. She goes in to take a shower but he barges in. If you look real closely, she is wearing underpants and is not nude although she is taking a shower.
Revealing mistake: In the scene where Bond is trying to escape with his new Mini-Jet, he flies through a big hall. If you look carefully, you can see that the aeroplane which is supposed to be flying with its wings vertical is fastened to some kind of sustainer.
Revealing mistake: At the beginning of the film, Bond is on a training exercise to free a trapped hostage. Since it is only a training exercise, everyone involved is using blanks in their weapons. Why is it that when Bond fires an automatic rifle, we hear multiple bullets ricocheting? (00:03:25)
Revealing mistake: When Superman gets blown away by the bombs, he is being smashed onto the rocks. You can easily see that the rocks aren't real, but also that when he rises up again, you can see the cardboard rocks dent.
Revealing mistake: In the scene in which Alan Shepard is about to land his jet on the aircraft carrier, the plane seen from the outside is a single-seat A-4 attack plane. But inside the cockpit actor Scott Glenn lowers his sunshade, and reflected on the shade can be seen the wings of a two-seat jet trainer, the T-33A.
Revealing mistake: When Nicole's bike jumps over the kids lying on the ground there's a ramp beside them disguised as part of the road to allow for the stunt.
Revealing mistake: During the Amazon women sequence, when Niki gets pulled underwater you can tell by the movement of the water that it was shot in reverse. (00:49:32)