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.
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.
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: 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: 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: At the end when the Wizard and Dorothy are in the balloon basket, the tie down ropes on the right side keep going from tied to untied and back to tied again through different shots.
Continuity mistake: When Dorothy is talking to the Scarecrow for the first time, the Scarecrow moves further down his pole between close up shots.
Continuity mistake: In the scene where the Wicked Witch in Munchkinland goes over to observe the ruby slippers on her dead sister's feet, when she is up close there's not much space between her and the slippers but when she turns around and says "they're gone," she's further away, then she's closer again in the next shot.
Revealing mistake: When the guard tells Dorothy that she may not see the Wizard, Dorothy starts crying and tells a sob story about Auntie Em. Then, it shows the guard crying, but the tears aren't coming from his eyes. They're coming from above his eyebrows.