Revealing mistake: When it starts to snow in the poppy field, Dorothy falls asleep, followed by the lion. In many of the later shots, a thin wire attached to the lion is visible the entire time.
Continuity mistake: During the tornado scene at the farm Dorothy runs to the back of the house and the bench is turned over - when she returns the bench is upright .
Continuity mistake: When Glinda tells Dorothy to follow the yellow brick road, there are many Munchkins around. A second later, when she is about to vanish, they've all disappeared.
Continuity mistake: When the Witch melts, four guards suddenly appear behind her remains.
Continuity mistake: When the Munchkin in purple tells Dorothy to follow the yellow brick road, Toto runs ahead of Dorothy. In the next shot he's back behind her.

Continuity mistake: When the Munchkins come out onto the Yellow Brick Road, one of them comes out of a sewer hatch on the yellow bricks. It's located on the ground in front of the first small white cottage with the thatched roof, right behind Dorothy's house. Throughout this scene, the dark hatch is visible whenever we see that specific location, such as when the Wicked Witch of the West asks, "Who killed my sister? Who killed the Witch of the East? Was it you?" but as Dorothy begins to "follow the yellow brick road", there is an overhead shot followed by a front shot and the dark hatch has disappeared.

Continuity mistake: Back in Kansas, Dorothy holds Toto and her pigtails swap from being behind to in front.
Continuity mistake: The Munchkin Mayor's watch keeps changing time, from nearly to the hour, to twenty after the hour.
Continuity mistake: At the end of the movie, when Dorothy sits up, from the side shot her hair is shown going down her back, but in the front shot, her hair is in the front.
Continuity mistake: When the companions are walking down the corridor to the wizard's room, Toto is on their left side. Then, the camera view suddenly cuts to being behind them, and in which case, Toto is suddenly on their right side.
Revealing mistake: Throughout the movie, the tin man's costume wrinkles up.
Other mistake: When Dorothy's house is falling back to Kansas, just before it lands, there is about a 1 or 2 second shot of what looks like production notes written in blue ink.
Suggested correction: There are no production notes visible anywhere.
Continuity mistake: When the Tin Man is telling his story, as he says "I was chopping that tree," Dorothy starts to look at the tree he's referring to, but in the next shot, she's looking right at the Tin Man again.
Continuity mistake: When Dorothy arrives in Munchkinland, she hugs Toto, but a frame later her right arm is extended.
Continuity mistake: In the very beginning of the film, as Dorothy and Toto are running down the road towards the farm, you can see a small grease spot on Dorothy's apron when she reaches down to pick Toto up. When they reach the farm, somehow the spot has vanished.
Continuity mistake: In the poppy field, when Dorothy points at the Emerald City, the Lion is standing more than a meter away from her. In the close-up he stands very close to her.
Continuity mistake: In the haunted forest, when the Tin Man is lifted up in the air, the Lion crouches and covers his face with his paws. A frame later he is standing up in a totally different position.
Continuity mistake: Aunt Em places a cold towel on Dorothy's head. The towel is sometimes away from the eyebrow, slightly on top, or completely covering it, depending on the angle.
Continuity mistake: The Lion says, "Read what my medal says," and holds it with his paw. In the close-ups the paw is away and the medal lies flat on his chest.
Continuity mistake: When water falls on the witch, a guard on the left disappears.