Underarm hair error
During Walkabout's central swimming scene, there are two shots in which The Girl's underarms can be seen to be quite clean-shaven: the shot in the middle of the scene in which she stands up in a shallow part of the pool and pushes her hair back, and the shot at the end of the scene in which she's putting her blouse on.
Of course this makes virtually no sense, since there's almost no imaginable reason she'd have brought a razor with her on the outing that ended with her and her brother getting lost; nor is it likely she'd have bothered using such a razor, if she'd had it, while wandering around in the Outback.