"And what does it *need*?" she asks naively.
"It needs to cum!" you snap.
"But why?" she asks, puzzled.
"I don't know," you say angrily. "I guess the sperm all builds up when my body feels it may have a chance to impregnate a woman..." then you realize that you don't really want to anger her, and you say more softly: "especially such a very beautiful woman..."