This easy-to-do but very frightening trick is called the “Colorado Skalbagge” (Colorado Beetle).
And my Grandmother Valborg used to LOVE it. She always had one loaded incase a guest would stop by.

Here is all you need:
An envelope
A button
A rubberband
A hair pin

“Open” the pin into a V and pull the rubberband through the holes of the button and attach it to the pin. See picture.
Spin the button. For every turn it gets tighter and eventually it will be forced to spin back if you would let it go.
This is the effect you want, when it is forced back like that you should slide it into the envelope and close it.

Then simply hand the envelope over to your victim and say:
“Hey, I found a Colorado beetle. Have a look!”

Hopefully the twisting button will scary their socks off when they open the envelope.

Viola loves it and tries to scare everyone who comes in her way.

PS: I guess there are many names to this trick!? Have you heard of it before but under a different name DO please let me know! I would love to hear it!