I've always heard that there is a scene missing from some of the opening day prints of Star Wars. I believe it was the part where Han & Luke are taking Chewie as a prisoner transfer & Chewie growls at the little robot on the floor of the Death Star. Is this true? Or is it along the same lines as the second throw of the grappling hook?
Yes, that scene was rumoured to have been missing in some early showings of Star Wars in 1977. From IMDB:
There are at least two different prints of the original Star Wars in circulation. One definite difference between them is that the brief scene in the Death Star corridor where Chewbacca roars and "frightens" a little messenger droid is missing. This scene was NOT in the "opening day" version.
It is just another rumour, along the lines of the grappling hook miss and the rebel hangar conversation about Luke's father being present in some prints.
I think people invented this rumor as this scene was one of the many unscripted gags that they filmed. Most were cut out, but this one made the final cut. Since this small moment isn't in the shooting script or the novel, perhaps people transferred their memories of this shot being gone in the books to being gone from the movie at one time as well.