Continuity mistake: When Tweedle Dum and Tweedle Dee are telling Alice the story about the walrus and the fisherman, when the walrus has the oysters in the hut and he looks at the menu it is right ways up telling you that oysters are being served. He then places it upside down on the table so the menu should be upside down writing however when the next shot comes in the menu is the right way up.
Continuity mistake: When we see the box of cakes appear in front of Alice, it shows us Alice is sitting on an orange tile on the tiled floor. It cuts to a wider shot and she is now sitting on a black tile.
Continuity mistake: When Alice enters the White Rabbit's home, a grandfather clock is present near the door, by the foot of the stairs. But when her leg starts growing, and it goes down the stairs, the clock is nowhere to be seen.
Revealing mistake: When Alice tells the Mad Hatter how she appeared in Wonderland the hare's paw is superimposed on the teapot's handle as if the pot were flat or he was floating.
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: In the song 'painting to roses red', after Alice sing 'Oh, pardon me, But Mister Three Why must you paint them red?' the three cards say 'Huh? Oh!'. When they say that, The three of clubs card has a three in the bottom right corn with no clubs symbol on top of the three. the three of clubs also has nothing in the top left corner. The Ace and 2 of clubs have nothing in both of there corner. A few slides later, the symbols in the corners come back.
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.
Audio problem: After the flowers pour a load of water on Alice and she slides down, she says "they could learn some manners" but her mouth is not in sync.
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: 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.
Deliberate mistake: When Alice is about to meet the queen she hides the brush covered in red paint under her dress. The brush later disappears plus Alice doesn't have any stains on her clothes.
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.
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