A prominent Polish scientist conducted very important experiment.
He trained a flea to jump upon giving her a verbal command ("Jump!").
In a first stage of experiment he removed flea's leg, told her to jump, and the flea jumped.
So he wrote in his scientific notebook: "Upon removing one leg all flea organs function properly." So, he removed the second leg, asked the flea to jump, she obeyed, so he wrote again: "Upon removing the second leg all flea organs function properly." Thereafter he removed all the legs but one, the flea jumped when ordered, so he wrote again: "Upon removing the next leg all flea organs function properly." Then he removed the last leg.
Told flea to jump, and nothing happened.
He did not want to take a chance, so he repeated the experiment several times, and the leg less flea never jumped.
So he wrote the conclusion: "Upon removing the last leg the flea loses sense of hearing"