When I worked as a clown I had a bit I did for younger kids, "The Flea Circus", in which with a concealed pencil and sheet of plain white paper I'd try to persuade a group of suspicious 5 year-olds that there were indeed fleas doing all sorts of acrobatics and stunts. They were pretty skeptical, but with my free left hand hidden under the paper playing the role of "Escaped Flea", dispensing abundant pinches to the unbelievers, I managed to bring them all back into the fold...
Imagine my surprise when I found out there was actually such a thing!
Links: Wiki on the Flea Circus, http://flea-circus.com/
Videos: https://www.youtube.com/watch?v=r9BjN_GHIic, https://www.youtube.com/watch?v=SQLPhS1N9pc