Ask a spectator to come up on stage and tie two small wooden blocks, which are connected by means of two ropes, around his waist. One block is lying on his stomach, the other on his back. Next, drill a tiny hole, very loudly, through the two wooden blocks and (allegedly) through your 'victim’s’ body. Push a plastic tube, via the wooden block, into the spectator’s stomach and stick a second tube (+ a funnel) through the block on his back. Next, show the audience that the two tubes, in the spectator’s body, are joined together. For that, pour a certain amount of water into the funnel and look ... the water finds its way through the spectator’s body and re-emerges, via the small tube, at the front. Catch it there in a bucket, otherwise it could be a very wet business! In the theatre too, it will, by now, have become a bit damper, but that will have more to do with the tears of laughter...