Continuity mistake: After Alice's foot bursts through the rabbit's house, he moans and growls and suddenly disappears a shot later.
Continuity mistake: At the mad tea party Alice is sitting between the Mad Hatter and the March Hare, but when the March Hare bonks the Mad Hatter on the head with a hammer Alice is sitting next to the Hare who is now sitting next to the Hatter.
Continuity mistake: When the King smashes the Queen's crown with a hammer, it has 5 half-arches. A shot later it has 6.
Continuity mistake: After the broom-dog deletes the red road a huge rock suddenly appears in front of Alice.
Continuity mistake: When Alice eats the cookie in the rabbit's place her foot grows huge along the stairs, down to the entrance and out to the garden without knocking a single object except the poor rabbit. When the angle changes to a shot outside the house suddenly all of the furniture has magically appeared out of nowhere next to the shoe.
Continuity mistake: While sitting on the branch Alice's cat suddenly disappears only to reappear in the following shot. A shot later, Alice sits down and she reaches for the cat who is at arm's length.
Continuity mistake: The names Tweedle Dee and Tweedle Dum embroidered on their collars disappear between shots.
Continuity mistake: The lizard's ladder suddenly becomes really long.
Continuity mistake: This occurs when Alice is near the cards during the painting the roses red scene. When they say "ooohh" the two & the three are next to each other, the shot goes to Alice then back to the cards and the two and the ace are now next to each other. (00:55:45)
Continuity mistake: After being pulled toward the Rabbit's Cottage by the White Rabbit, Bill's feet change. They change back when the ladder is being set up (almost exactly 10 seconds). (00:23:09)
Continuity mistake: After giant Alice grows inside the rabbit's house the tree by the front door has branches growing to the left. A shot later it also has branches growing to the right.
Continuity mistake: When Alice grows inside the rabbit's house and her foots bursts outside, her soles swap from black to light brown.
Continuity mistake: When Alice's sister wakes her up Alice puts her right hand behind the cat. A shot later it's next to his back.
Continuity mistake: When the king says he needs witnesses to judge Alice, the pile of books changes position in every shot.
Continuity mistake: When the Cheshire cat reappears to show the way to the Queen's castle the branch on the right keeps changing style in almost every shot. It doesn't have to do with fantasy, dreams or anything plot-wise.
Continuity mistake: The handwriting on the "Don't step" sign changes between shots, specially the apostrophe on the first sign.
Continuity mistake: When Alice sees the first sign of the sentence "Don't step on the mome raths", it has 3 nails, one on the middle upper part and two on the middle lower part. A shot later there are just two nails on each opposite side of the upper part.
Continuity mistake: When Alice leaves the Hatter and Hare the wide shot of them toasting not only does it not show all the mess they've made, but it is the exact very first shot we saw of them when Alice arrived.
Continuity mistake: When the Mad Hatter squeezes a lemon on the clock, jam is spread all over the machinery. A shot later there's just a small pile of jam.
Continuity mistake: When the Mad Hatter pours jam in the clock the mess on the table disappears. Also, all along that scene the objects around are not continuous between shots.
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.
Guy