Funny story taken from the flying cow bulletin:

As a resident physician in radiology, I was speaking with the man whose wife was about to receive a CAT scan of the chest. While the nurse was placing the intraveneous line, I asked the husband if his wife had undergone any more test's. The man named several procedure's involving various body part's, but he couldn't remember one particular test. Thinking out loud, he said, "What is the thing that women have that men don't?" His wife was quick to answer, "A brain, dear."