Revealing mistake: In the soda shop, the waitress turns off the lights with her elbow because her hands are full, but she misses the light switch by 6 inches. (00:55:10)
Revealing mistake: During the subway scene, when the first pillar breaks and starts to move towards Dorothy, the top of it is cardboard and wiggles back and forth as the pillar breaks. This is noticeable in the other pillars as well.