Other mistake: In the opening credits, Lewis Carroll is spelled incorrectly, as 'Carrol'. (00:00:30)
Other mistake: After listening to the flowers sing, Alice is standing and talking to them. Although Alice is moving her head and arms around, her shadow stays still.
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