This is one of the all-time greatest gags! You show an envelope with the words Rattlesnake Eggs. Explain that the weather has been right lately so they would not yet be nearing the hatching stage, and it is safe for them to take a look. When you hand it to your victim and they open it...the envelope vibrates wildly (and loudly!) Scares the bajeezus out of them, completely harmless, and re-usable!