Seems impossible- and it happens right in front of their eyes!
You show your spectator a metal tube, a pen and a tiny little steel ball. The tube has a hole right through it, about in the middle of the tube. The pen is pushed thru the hole so that it passes right thru the tube, blocking the interior of the tube and preventing anything from passing through the tube. The ball is then dropped into the tube. Of course, it gets struck in the middle of the tube because the pen causes an obstruction. But once you make your "magical gesture", you agin drop the ball into the tube. This time, the ball goes right through the tube- and right through the pen! And if they couldn't believe their eyes the first time, you pass the ball right through again! At the end, you remove the pen from the tube, show that the tube is empty, and the pen is solid. HOW DOES THIS WORK??You will have to get one to find out!
Tube is made of metal.