I don't know what made me think of it today, it's very old but here goes.
A man called an escort agency and requested a tall, slim red headed woman. When she turned up he asked her to strip off and kneel on all fours in front of the fire. She was a bit peturbed but did as she was asked. He said he wouldn't be a moment and left the room, returning a few minutes later with a Red Setter and saying:
"You see, that's what you'll look like if you don't eat your dinner!"