A little background before I explain the intricacies of this quirky little practical joke. Our pastor had one of these little envelopes which he kept in his desk drawer. Once when we'd stopped in to see him, he asked if he could show me something he'd picked up on a trip out West. He pulled out the envelope and handed it to me. I opened it, looked inside, and proceeded to scream loud enough to bring in the church secretary.
In this envelope was a clever little device made out of a washer, a rubber band, and a piece of metal that looked like an untwisted paper clip. The rubber band was wrapped around the washer and metal piece and then twisted in such a way that it stayed flat in the envelope; however, once you open the envelope, it unwinds and sounds disturbingly like a rattlesnake. Your head says that a real snake couldn't be in there, but the noise and movement cause you to think otherwise.
This afternoon, while cleaning out two of our junk drawers in the kitchen, my youngest found the two envelopes. Very wary, she took it to her older brother, hoping he could explain what it was. He shook the envelope and acted startled. Her response: top of the lungs screaming, stomping up the stairs, and slamming the bedroom door. Who knew that she was so afraid of snakes? I tried to calm her down, but I didn't hide my chuckling very well. It helped when I explained my reaction to the same trick.