Inform a friend, on the way to swim lessons, that you have a fascinating story for him and could you please just see his hand? Procure a pen and draw three tiny stick figures on top of his hand. Tell him: "There were three men having a walk. One was blind, one was dumb, and one was deaf. Here goes the blind one (draw the man's trajectory up the arm)--tell him when to stop." Break off the line when your friend says stop. "Here goes the dumb one. Tell him when to stop." Same thing again. "Here goes the deaf one. Tell him when to stop." Your friend will do so. He will become alarmed when, instead of stopping, you scribble all the way up his arm, lacerating it because you're digging so hard. The man is deaf you see. He cannot hear.

You don’t have to be on the way to swim lessons, but the man must be deaf.