Nathan: (petting Brutus) "It's Brutus milk." (points to the cat's belly)
Me: "No, Brutus doesn't have milk. Brutus is a boy. Only mommies have milk. You're a boy."
Nathan: "No. I'm not a boy. I'm Nathan."
Me: "Yes, you're a boy! And Daddy's a boy."
Nathan: "No, he's Daddy."
Me: "Daddy is a boy. And Jacob's a boy, too."
Nathan: "No, he's Jacob."
Apparently he hasn't grasped the concept of gender yet. And I wasn't up to an anatomy lesson.