Tommy Rettig's changing hair style.
The film suffers from some jarring continuity errors that somehow were not noticed in the cutting room. During the last third of the film, Tommy Rettig's hair goes from being long and fair, with a fringe, to being short back and sides and dark and brushed back and then changes back again on two occasions, once in the same scene. If I'd been Delmer Daves, I'd have been too embarrassed to release the film until that was put right, as it would have made me look a right fool.
It seems that what may have happened here is that Tommy's hair was short, combed back and naturally dark and that he wore some kind of fair haired wig throughout most of the film, but that here and there, he didn't wear the wig when filming a scene. Because scenes in films are not generally shot in the right sequence as they appear in the script, when the sequences are put in the right order in the cutting room, you get the strange effect of his hair changing in colour and length from shot to shot in the same scene.