Daughter: (swimming about in my large jetted bathtub) "Mommy...what are nipples for?"
Me: (flossing my teeth thoughtfully in front of the mirror) "Well, remember how we've been reading about mammals in your science books? Remember how Mommy mammals use them to feed their babies?"
Daughter: "But what are Daddies' nipples for?"
*And I promise I didn't make this one up to get more Gooogle hits!