15 things you don't know about your penis.

1. Smoking can shorten your penis by as much as a centimeter. Erections are all about good bloodflow, and lighting up calcifies blood vessels, stifling erectile circulation. So even if you don't care all that much about your lungs or dying young, spare the li'l guy.

2. Doctors can now grow skin for burn victims using the foreskins of circumcised infants. One foreskin can produce 23,000 square meters, which would be enough to tarp every Major League infield with human flesh.