Continuity mistake: After the Tin Man's dance, Dorothy and the Scarecrow shuffle over to a tree trunk where the Tin Man then sits. During this, the oil can in Dorothy's basket clearly falls out, but in the very next shot it is back in the basket.
Continuity mistake: During the sequence where Dorothy meets the Scarecrow, Dorothy's pigtails are first short (above her shoulders) and as the song progresses her hair gets longer (below her shoulders), then short, and then long again.
Continuity mistake: During the scene when Dorothy and Scarecrow are fighting with the trees, Scarecrow says "I'll show you how to get apples" and he gets hit by the apples. In the very next shot, a quick view of Dorothy reveals she is wearing black shoes, not her ruby slippers.
Revealing mistake: When the Lion is pulling up the Tin Man with his tail on the way to the castle, you can see a square block inside the Lion's costume to hold the tail on.
Continuity mistake: In the scene where the Wizard is about to bestow 'awards', the Scarecrow is lined up second from the left as the Wizard begins to speak. In the next shot while the Wizard is still speaking, the Scarecrow 'jumps' to the far right.
Continuity mistake: When Scarecrow, Tin Man, and the Cowardly Lion are marching into the Wicked Witch's castle after taking the guards' uniforms, all three of them are shown holding the same types of spears as the guards, so when they go rescue Dorothy out of the locked room and Tin Man chops through the door with his axe, where did the axe come from?
Revealing mistake: When everyone is still in the poppy field, after the snowstorm, Dorothy says "Look. Emerald City is closer and prettier than ever." Look behind the Lion just as Dorothy says the word "City" and you'll see that the wire attached to his tail brushes over the top of some of the poppies, knocking the snow off.
Audio problem: When Dorothy, Scarecrow, and Tinman are in the forest where they find Lion, the first time Dorothy says "Lions and tigers and bears, oh my" her mouth doesn't move at first but when the camera cuts to the next shot her mouth finishes the phrase.
Revealing mistake: Soon after Dorothy slaps the Cowardly Lion, she looks as though she is about to laugh out loud. This happens about 10 seconds or so after the slap. She even tries to put Toto in front of her face to cover up her smirking.
Continuity mistake: As the chandelier falls on the guards at the witch's castle, all the candles are blown out by the time it lands. The next shot shows some of them relit.
Continuity mistake: Immediately after Dorothy throws the water onto the witch, there is a long shot of the group as they observe the Wicked Witch beginning to melt. In this shot you can see that the Scarecrow's arm is still on fire, yet nothing is done about it as they all focus on the Witch. In the next full shot of the Scarecrow the fire is completely out.
Continuity mistake: Dorothy's hair is long and almost straight in some shots and short and curly when the camera pans back to her. This happens throughout the movie.
Continuity mistake: In the beginning while Dorothy is still on the farm, she walks along the pig pen fence and then falls in. When Bert Lahr picks her up out of there her dress is perfectly clean.