A 27 cm long, 5 cm wide, white plastic strip is shown from both sides. It has a large hole at the top. You bring this up to your eye, squint the other eye, and look through the opening at the audience. Then you bring both ends of the strip together and release one. It immediately springs back to its original position. This proves that it is made of solid material.
Now hold the strip with your right hand at the bottom and your left hand at the top. The thumb and index finger of your left hand reach into the hole, and something incredible happens:

Your left hand moves downward, visibly pulling the hole down with it! Then turn the strip over again, look through the hole as before, and then throw it to the audience for inspection. It's unprepared!