Where does milk come from?

Lately TK has been asking all those bazillion little questions. He will be 4 soon, and I think he's increasing the frequency of the questions in order to have them answered before the big day.

Usually they are simple and answered quickly with little thought on my part.

Where do apples come from? Trees.
Where do trees come from? Seeds, then they grow.
How many teeth do I have? Let me count...1, 2, 3 um 15.
Can I have more Chocolate milk? No, you had some 5 minutes ago and you just brushed your teeth.

But then yesterday in the grocery store.
Where does milk come from? Ah...well...from cows. Yeah, cows. Farmers milk them.

Whew, I was glad he took that answer! I was preparing to explain the ins and out of teats and babies drinking their mother's milk and yes you too drank your mother's milk, and yes my milk came from teats, oh those are called breasts...

Maybe that's a 4 year old question? And maybe the older siblings will be the ones to field that question, if I'm lucky.