Continuity mistake: When being a giant inside the house, Alice extends her arms and they're quite short. A couple of shots later she remains the same size but her arms are now 5 times longer to allow for her to open the windows on the front. This has nothing to do with the magical cookies.
Continuity mistake: When Alice becomes a giant she slams her right foot on the door. A shot later she is lifting her left foot.
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: After Alice's foot bursts through the rabbit's house, he moans and growls and suddenly disappears a shot later.
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 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: After the broom-dog deletes the red road a huge rock suddenly appears in front of Alice.
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.
Continuity mistake: When the Mad Hatter smashes the clock its distance to the teapot next to it increases between the first and second shot.
Continuity mistake: When Hatter and Hare cry "move down" the spoon, the yellow cup and saucer in front of Alice disappear.
Continuity mistake: When the Mad Hatter shouts "Pick up" Alice is given a yellow cup. The white and pink cup in front of her suddenly disappears 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