Where Are Your Nipples?

I know I'm supposed to be the one answering questions not asking them, but I have a question for all of you out there reading this blog which I would like your help answering. How do human beings know exactly where their nipples and belly button are at any given time? How, regardless of your surroundings, are you capable of putting your finger tip right on your nipple and being positive of where it is? Is that strange to anyone else?