Revealing mistake: Right after Dorothy slaps the lion, there is a green smudge on her arm. Looks like the witch's makeup. (00:50:35)
Suggested correction: There is no "green smudge" on her arm. Perhaps this is referring to the blue mark that appears on her arm as she talks to the lion? Because I'm not seeing anything on her arm that is green.
Revealing mistake: When they first meet the Cowardly Lion, he jumps off of a boulder and obviously lands on a trampoline and jumps off.
Suggested correction: There is no trampoline visible. Sure, there is most definitely something he jumps off that is hidden behind the plants, but since we don't actually see it on screen, I don't see how it's a mistake.