The classic gag, available for sale from Adams--an envelope of "rattle-snake eggs":
You wind up the washer on the rubber band (in this version, the wand that holds the rubber band even looks a little snake-like), carefully place into the envelope, and hand to someone to inspect. When the envelope is opened, the washer, powered by the rubber-band, spins against the paper, making a loud rattle that should scare the bejezus out of the victim.
This clip-art detail from the packaging provides a close approximation of the victim's reaction:
The one pictured here was purchased at Disneyland for only three bucks. Who says you can't find a cheap souvenir at Disneyland anymore?
And if you don't want to part with three bucks, you can make the gag yourself with a pair of paper clips and a rubber band. Here's the directions, courtesy of "Spooky Stuff" (1979, Shari Lewis), a children's book of Halloween party hints and tips.
The author is former TV-kids show host and Lamb Chop puppeteer Shari Lewis. Shari recommends inserting a rattler gag with each party invitation you send out. Nice. I'll be revisiting "Spooky Stuff" in later posts.
2 years ago