Crazy behaviour.

In olden days, felt and other hats were prepared with the aid of mercurous nitrate, a highly toxic substance which can produce a tremoring disease similar to Parkinson's disease. Such people were assumed to be mad. The most famous Mad Hatter is in Lewis Caroll's Alice in Wonderland, but the original is thought to be the 17th century Robert Crab, an eccentric who lived in Chesham, who gave away all his worldly goods to the poor and lived on dock leaves and grass.