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. (00:03:45)
Revealing mistake: When the Wicked Witch scares the Munchkins in Munchkinland, where Dorothy lands, she disappears into a cloud of smoke she creates. But you can see her sneak down into a trap door below. [As a sidenote to this entry, Margaret Hamilton was hospitalized for severe burns after a take of this shot (not the final one used) when the stage elevator got stuck and the explosion went off.] (00:30:45)
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. (00:40:15)
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. (00:35:15)
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. (00:48:45)
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. (01:20:00)
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. (01:08:00)
Continuity mistake: When trying to escape the Witch's castle, the big doors close, and the gang stands in a line and starts banging on the doors. Between shots, Dorothy and the Tin Man switch sides. (01:21:15)
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. (01:24:50)
Continuity mistake: When the Witch melts, the broom is laying several inches from her dress. In the next shot, the broom is practically touching her dress. (01:26:20)
Continuity mistake: When the Wicked Witch scares the Scarecrow, Dorothy, and the Tin Man with fire, after the fire is thrown, not only is the Tin Man's funnel cap on backwards, everything is reversed. In order to keep the characters oriented from left to right correctly, they had to show the film from the wrong side, thus the buttons of the Scarecrow's jacket and everything else are on the wrong side. (00:46:40)
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. (00:45:25)
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. (01:34:55)
Continuity mistake: After both Dorothy and Scarecrow have oiled Tin Man's elbows, Dorothy pulls the Tin Man's arm down and we see her throw the apple that she's holding down behind him. In the next shot it reappears in her left hand. (00:41:55)
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.
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. (01:29:10)
Visible crew/equipment: While Dorothy and the other characters are cornered in the Wicked Witch's castle, when Dorothy grabs the bucket of water and tosses it at Scarecrow's arm, the water hits the Witch. In the closeup of the Witch's face, you can see a crew member's hand (a long sleeve can be seen at the wrist) in the upper left side of the shot. (01:26:20)
Revealing mistake: During some scenes, straw-stuffed Scarecrow's pant legs and his boots would sometimes have a gap that reveals the skin of Ray Bolger's leg. Two examples are, at Emerald City when Scarecrow places Lion's "cape" on him, and also when Dorothy and her friends are told the Wizard says to go away. (01:05:50 - 01:07:25)
Visible crew/equipment: The seams in the floorboard under the Haunted Forest set can be seen several times under the leaves. The best is in the close-ups of Toto. (01:15:30 - 01:19:35)
Continuity mistake: The Tin Man starts chopping the Witch's door and it's not the same one we just saw three shots before. The wood is a different color and the dark metal brace has been polished in the close-up. (01:23:40)
Answer: In the film it's left ambiguous. At the end it's strongly implied that she was dreaming. The characters she meets all look like people she actually knows. In the original book, she actually went to Oz.