Deliberate mistake: The Fremen wear "stillsuits" to conserve their water, yet leave their heads completely uncovered. This would result in quite a bit of water loss through perspiration. (In the book, they wore hoods, masks and nose filters, leaving only the eyes uncovered, but it wouldn't work in a movie to have all the actor's faces obscured!).
Dune (1984)
1 deliberate mistake - chronological order
Directed by: David Lynch
Starring: Max von Sydow, Patrick Stewart, Brad Dourif, Kyle MacLachlan, Jose Ferrer, Francesca Annis, Sting, Leonardo Cimino
Continuity mistake: Depending on the version, in the final confrontation between the Emperor and the Harkonnen, and Paul and the Fremen, you can see Thufir Hawat standing in the crowd of the imperial side. After the battle between Paul and Sting he has suddenly disappeared. This is due to there being different, much longer versions of the same film. There is a 120 minute version, 180 and 190 minutes, and apparently in Singapore you can buy a 240 minute version. However, in the long versions the stains on Thufir's lips and Paul's totally blue eyes do not appear in the extra scenes: now you see it, now you don't.
Guild Navigator: We ourselves perceive a slight problem within House Atreides. Paul, Paul Atreides.
Padishah Emperor Shaddam IV: You mean of course Duke Leto Atreides, his father?
Guild Navigator: I mean Paul Atreides. We want him killed. I did not say this. I am not here.
Padishah Emperor Shaddam IV: I understand.
Trivia: The tendons on the worm when it gets hooked by Paul are made from condoms.
Answer: Because it was edited in a way he didn't approve of. The film was actually over 3 hours long, and it was trimmed by about an hour for the cinema version, and then a certain amount of pick and mix went on to come up with the video version.
David Mercier