Continuity mistake: In the beginning of the movie Dorothy comes running into the farm and there's an old tire hanging from a tree. Two shots later as she walks away from Aunt Em and Uncle Henry the tire has been moved. The angle at which it hangs has been changed and the piece of rope hanging on the bottom of it is now three or four inches closer to dead center than it was before. (00:03:00)
Continuity mistake: As Toto escapes from the Wicked Witch there's a mortar and pestle to the left of the hourglass. In a close-up Dorothy looks at the hourglass after the Wicked Witch turns it over and we see the pestle has been moved to the other side of the mortar. There will be no confusion about this if you look at the direction of the shadow cast by the hour glass. (01:18:20)
Continuity mistake: Dorothy's Aunt hands out some food, walks with her and leaves Dorothy alone. Several meters ahead there's a cart wheel and one chicken. When the angle changes, Dorothy is standing next to the wheel, which is also facing a different position, and there's a lot of chickens around.
Audio problem: After the witch says "Well my little pretty, I can cause accidents too." her mouth starts to move again but nothing is heard.