A man and a woman were waiting at the hospital donation center.

Man: What are you doing here today?

Woman: Oh, Im here to donate some blood. Theyre going to give me $5 for it.

Man: Hmm, thats interesting. Im here to donate sperm, myself. But they pay me $25.

The woman looked thoughtful for a moment and they chatted some more before going their separate ways. Several months later, the same man and woman meet again in the donation center.

Man: Oh, hi there! Here to donate blood again?

Woman: [shaking her head with mouth closed] Unh unh.