Continuity mistake: When the four are at the end of the hallway to see the Wizard, Toto is near the lion's feet. As it switches shots, he is behind The Tin Man.
Continuity mistake: There are two actresses playing Dorothy (and two dogs playing Toto) as she opens the door to Oz. The first is a stand-in wearing a dull colored dress in order to make it look black and white. After she opens the door and moves out of the way, Judy Garland is who we actually see walking through. Look at the different pleats on the two dresses. (00:19:25)????