Visible crew/equipment: After Dorothy returns from Oz, we see her laying on the leaves in the woods. In an extreme closeup of her eyes, the camera is reflected in them. (01:37:10)
Factual error: When Dorothy runs away from the hospital she is chased by a nurse, who has a torch. Earlier in this film the doctor said they two months away from the 20th century which gives the year as 1899. Such a modern torch that the nurse had was not invented yet.
Continuity mistake: When Dorothy finds Tik Tok, there are cobwebs that hang from the wall beside him, and are draped on the side of Tik Tok's metal helmet. However in some shots these cobwebs that hang on his helmet vanish, then reappear again.
Continuity mistake: When Tik Tok takes the lunch pail from Dorothy, to use it to attack the Wheeler's, his arm is naturally shiny. Moments later the same arm suddenly has cobwebs all over it. Then when Tik-Tok gets to the end of the corridor, the cobwebs are gone again.
Continuity mistake: When Dorothy picks up the key that she thinks was sent from Oz, she begins to rub the dirt off of it, getting her fingers dirty. In the next shot they're clean. In addition, the way she holds the key changes between shots.
Continuity mistake: When Dorothy is sent back to Kansas, she wakes up in the forest and she has a large spot of dirt on her forehead. This vanishes when Toto runs to her. It then reappears later, but now on the side of her forehead.
Continuity mistake: When Tik Tok is just about to swing the lunch pail into Mombi, he freezes because his action winds out. In the next shot his position (his left arm, and the angle and way that he holds the lunch pail) changes between shots.
Revealing mistake: When Mombi's headless body wakes up and begins to walk towards Dorothy, you can see a black, blurry haze around her neck in two shots, where an effect was used to remove it.
Continuity mistake: When the Doctor is setting up the machine for Dorothy, the power then goes out. Everyone leaves. If you look at the machine, it's 'tounge' is on the right side of it's 'mouth.' In the next shot it is now on the left, and it then stays there.
Continuity mistake: When Dorothy and Billina stand in the crate, after the storm, trying to figure out where they are, in overhead wideshots of them standing in the crate, Dorothy's dress rustles in a breeze, but in closeups of her, it is perfectly still.
Continuity mistake: When it shows Dorothy eating her Limestone cake with Tik Tok and Jack, in one shot her goblet of melted silver is rested, down on the table, but then suddenly in the next shot it is in her hand, off of the table.
Continuity mistake: Aunt Em opens Dorothy's bedroom door a crack to check on her. She is standing outside the room, but she is peeping through the crack. Dorothy looks at her, and suddenly Aunt Em is standing in the room with the door almost fully opened.
Visible crew/equipment: When Dorothy is strapped down to the pedestal by the doctors, they then proceed to push her down the hallway, and pass the camera on their way. As they pass, the camera casts a clear shadow on the sheet covering Dorothy.
Visible crew/equipment: When Dorothy is speaking to Aunt Em about the key she found, Aunt Em says "That legs mended, it's mended..." then she gets up and passes the camera, which casts a clear shadow on her as she walks past it.
Continuity mistake: After Dorothy winds Tik Tok up (after he had gone beserk) her pigtails alternate from what shoulder they hang over (ie. her right pigtail was hanging behind her shoulder in the first shot, but then hangs in front of it in the next shot.)
Continuity mistake: When The Nome King shows his ruby slippers to Dorothy, and tells her that he could send her back to Kansas, in frontal shots both his feet are down on the floor, but in shots from behind he is wiggling his right foot up in the air.
Revealing mistake: When Mombi's headless body awakens and sits up, in the first two shots it is easy to notice that her body is actually simply a puppet of some sort, as the motion is not very fluid and it looks like a mannequin. Once she stands up, she becomes an actress whose head has been removed with special effects.
Revealing mistake: When Dorothy steals the key from Mombi's cabinet, as Mombi's body picks up her head to put on, you can see a small error. As Mombi lifts up her head, you can see the bottom of the cabinet warp slightly for about two frames (slow motion helps but is not needed), revealing that the actress simply had her head through a hole in the bottom of the cabinet (to make it appear severed), and her shoulders bumped into the bottom, making it shake/warp for a second.
Continuity mistake: On The Nome King's mountain, everyone looks up, and Tik-Tok is standing closest to the edge, then the sofa-body of the Gump is there, then Dorothy on the other side of it. In the next shot Tik-Tok is suddenly beside Dorothy.
Continuity mistake: When it shows the chickens on the farm, just before Toto runs over and scares them all, the position of the brood of chickens is completely different between shots, and the branches and logs around them have also changed around.
Answer: She was in the human world so she was in disguise.