|Postcard of the Tivoli Flea Circus contributed by Dan Goodsell|
Fleas have the capability to jump astronomically high in comparison to their body size. They can jump 13 inches horizontally, which is 200 times their body length!
In order to train a flea circus, you place fleas in a jar and put a lid on the top. The reason for this is to teach the fleas that they cannot ever jump beyond the length of the glass jar.