Show the brass tube and the steel ball- the ball is clearly too large to fit in the tube. However, on your command, the ball slowly sinks down into the tube. Now on your command the ball slowly rises back to the top of the tube! But when your spectator tries to perform the trick, they will not be able to get the ball to go into the tube - it won’t fit!
This incredible pocket illusion works on a different principle than the classic Steel Ball and Tube- this will fool magicians! Best of all, it's really easy to do- no switching!