Continuity mistake: When Alice arrives at the rabbit's house a watering can appears on the right. Also, the fence runs straight in the wide shots, but a door in between two rabbit sculptures appears in the close-up.
Continuity mistake: The names Tweedle Dee and Tweedle Dum embroidered on their collars disappear between shots.
Continuity mistake: When Tweedle Dee and Tweedle Dum show up Alice says "do you think he should be hiding?" and the flowers on the grass next to the tree disappear.
Continuity mistake: The way Alice holds the 'Drink Me' tag differs between the wide and close-up shot.
Continuity mistake: When the movie begins, Alice says "Nonsense" and sits the cat on the white part of her skirt. Wen the shot changes the skirt is blue. Then the angle changes and the skirt goes back to white.
Continuity mistake: After shrinking, a box appears on the floor between Alice's legs. She opens the box and takes out a cake. In the next shot, the box has disappeared.
Continuity mistake: After Alice's foot bursts through the rabbit's house, he moans and growls and suddenly disappears a shot later.
Chosen answer: There is no real answer. It is intended to be left unknown. See http://www.straightdope.com/classics/a5_266.html for The Straight Dope's answer.
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