How High Can You Jump?

Flea trainers have observed a strange habit of fleas while training them. Fleas are trained by putting them in a cardboard box with a top on it. The fleas will jump up and hit the top of the cardboard box over and over and over again. As you watch them jump and hitthe lid, something very interesting becomes obvious.The fleas continue to jump, but they are no longer jumping high enough to hit the top.