A little morning humor

One night a man and a woman are both at a bar knocking back a few beers. They start talking and come to realize that they're both doctors. After about an hour, the man says to the woman, Hey. How about if we sleep together tonight. No strings attached.
It'll just be one night of fun. The woman doctor agrees to it. So they go back to her place and he goes in the bedroom.
She goes in the bathroom and starts scrubbing up like she's about to go into the operating room. She scrubs for a good 10 minutes. Finally she goes in the bedroom and they have sex for an hour or so.
Afterwards, the man says to the woman, You're a surgeon, aren't you? Yeah, how did you know? The man says, I could tell by the way you scrubbed up before we started. Oh, that makes sense, says the woman.
You're an anesthesiologist aren't you? Yeah, says the man, a bit surprised. How did you know? The woman answers, Because I didn't feel a thing.