The dairy farmer has hired a young lady to help arounf the place. A couple of days later he says to her,

"The insemination man is coming today, I have put a nail in the door of the stall where the cow is to be done.  I have to go down to the paddock"

The guy duly arrives and she takes him down to the stall with the nail.

"Whats the nail for?" he asks.

" I suppose it's to hang your trousers on".