Norm, an old retired sailor, puts on his old uniform and heads for the docks once more, for old times sake. He engages a prostitute and takes her up to a room. He's soon going at it as well as he can for a guy his age, but needing some reassurance, he asks, 'How am I doing?'
The prostitute replies, 'Well Norm, old sailor, you're doing about three knots.' 'Three knots?' he asks. ' What's that supposed to mean?'
She says, 'You're knot hard, you're knot in, and you're knot getting your money back.'