My biggest gripe with the movie currently is that when a Crysknife is drawn it must draw blood before being sheathed again. If you don't use it on someone you must cut yourself. This is explained to the reader in the book, but in the movie it includes the scene where it would be explained but isn't mentioned. It's not a huge deal. They can just ignore it. However, at the end of the movie the Fremen have their knives drawn and it focuses on them cutting their hands to sheath them. I'm sure people who didn't read the books before seeing the movie would think it's really weird, especially for a culture so obsessed with water (although I don't recall if they've discussed recovering water from blood yet).