'Alice in Wonderland': Johnny Depp on why the Mad Hatter is really mad

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Johnny Depp went into great detail at the "Alice in Wonderland" junket on Saturday (Feb. 20) to explains his affinity for -- and his development of -- the madcap milliner, the Mad Hatter. 

Seems the hatter's crazy behavior -- and the phrase ' mad as a hatter' has a basis in fact. The mercury used in the trade of hat-making caused irreversible brain damage and it was common for hatters to develop mental, physical and emotional problems.