Continuity mistake: In one of the most endearing scenes from one of the greatest movies of all times, nobody noticed that as Dorothy sings "Over the Rainbow" the haystack she's standing next to just materializes between shots. Later it disappears long before the twister reaches the house. If you watch the movie you'll see the exact spot where the haystack should be seen as Aunt Em gives Dorothy a cruller and says to her, " and find yourself a place where you won't get into any trouble".
Revealing mistake: Soon after Dorothy, the Tin Man and the Scarecrow meet the Lion for the first time, they dance along the Yellow Brick Road, singing. As they disappear at the back of the set, their shadows can be seen on the backdrop, equally covering the trees and everything in between. DVD showing.
Revealing mistake: In the scene where Dorothy, Tin man, Lion and Scarecrow are in the haunted forest and are discussing whether or not to believe in spooks, Tin Man is lifted up into the air and then comes crashing to the ground. You can see his pants wrinkle up as he's trying to get up. Since when does tin wrinkle like that?
Audio problem: After the Wicked Witch of the West is liquidated, the soldiers hail Dorothy. After Dorothy asks for the broom, they are heard hailing her again, but none of their mouths move. As the scene fades into the next one, the soldiers' mouths can be seen beginning to move to say the line.