You set this trick pen up by inserting a plastic cap inside it and when someone takes the top off the pen it detonates the cap making a loud bang sound scaring the living daylights out of your victim!

The pen uses plastic caps (not supplied) to produce the bang. You need to buy the caps separately to use with this product, it won't work without plastic caps.  A google search for '8 shot plastic caps' will take you to them.

This product can be used as many times as you want, you just insert a new cap each time. The person who sets it off won't know what has happened until you tell them that they've been had!

They come packaged with instructions.

These are great fun for people of all ages to play with and they make great gifts.