“This packet really does contain old shattered rattle snake eggs. Did you know that they are worth lots of money…. They can even hatch if left in the sun?”
Your victim is curious and opens the packet… The packet hisses and rattles and jumps in their hands. Your victim will seriously wet their pants over this classic joke item.
The special gimmick that will frighten is easy to re-set so you can frighten hundreds of people.