.... of the hand and feet variety....
Fingernails grow three times as fast as toenails; as we age, nail growth slows; nails on the hand that predominates (i.e., left or right) grow faster than on the one that doesn't; nails grow faster in summer than they do in winter; men's nails grow faster than women's; and the rate of growth increases during a woman's pregnancy.
Why are such things known?
All from the NY Times' science pages - http://www.nytimes.com/2011/05/24/science/24qna.html?ref=science.
