Back when I was still in high school, my grandfather, a dairy farmer by trade, decided to make sure I had a clear understanding of the birds and the bees.

Grandfather:  Do you know how a woman gets pregnant?

Me: Yes, sir.

Grandfather: Do you know how a woman does not get pregnant?

Me: Yes, sir.

Grandfather: Good, remember that.

My take on this conversation – only abstinence prevented pregnancy.  Thanks to Steven Colbert of the Colbert Report, I now know there is one other sure way to not get pregnant – “Be a man”.