Polar Bear Nipples

I read a book to my son every night before he goes to sleep. He's been reading a bunch of non-fiction books lately. A few night ago, we read a book about polar bears. The book talked about baby polar bears getting milk from their mother. Boo Jr told me, "Polar bears don't drink milk. Milk comes from cows." I then explained to him that all mammals make milk and proceeded to list different kinds of mammals. I told him that if our dog, Sofie, had puppies that she would make milk, and told him that Mommy made milk after she gave birth to him.

"But where does the milk come from?" asked Boo Jr.

"Nipples." I said.

"Oh." my son said. And we continued on with reading our book.