I love word origins. The root of the term "mad hatter" is drawn from a time when mercury was used in the process of curing felt used in some hats. Over time the residual mercury would cause neurological damage (not the only damage caused by mercury toxicity of course). Given that anyone exhibiting an altered mental state was dubbed mad at the time, the cause of such malady, and subsequent death of such people doubtless went unexplained for a long time. Nice hat jerk bag!