Imagine, you show a wooden frame and a solid steel plate with a large hole in it. You show that the plate is in the wooden frame and you show that the plate cannot go any further if you place an object in the hole in the middle of the frame.
You pull the plate up again (clearly visible through the hole in the middle) and ask a spectator to put his or her hand through it. Then, when do you want to , you can press the steel plate down inside the frame, the spectator’s arm which of course stays neatly in place!
You remove the top half of the wooden frame and it is now clearly visible that the steel plate is around the arm of the spectator!
The steel plate may be considered safe and can be examined as well. ,The whole can be displayed all around and is extremely cleverly made..
Dimensions of the device, approx. 33 x 28 x 9 cm.