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

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.