Revealing mistake: At the first premiere (at Grauman's Chinese Theatre), look closely at the audience. Because at the end of the movie, and several months later at the premiere of The Dancing Caviler, it is the same audience! (Same clothes and even the same seats!)
Revealing mistake: When the Prince and Princess are catapulted over the wall of the Giant's castle, you can see their shadows on the "sky" above the wall; the sky is a studio wall painted blue.