In January 2009 someone asked where the phrase "screwed like a house cat" came from. All of the repsonses concerned actual house cats (Felis catus). Now, "cathouse" is a slang term for a brothel, so I got to thinking that if it's a cathouse, the employees could be called "house cats" and their professional duty is getting screwed quickly and often.
Original discussion:
http://www.phrases.org.uk/bulletin_board/59/messages/538.html