At one point Plato stated that man was merely “a featherless biped“. Diogenes, another famous Greek philosopher and Plato’s contemporary, didn’t agree with that, as he saw humans as more complex than that. To prove his point Diogenes plucked a chicken and sent it to Plato’s Academy to be enroled as a student. Then annoyed Plato added “with broad flat nails” to his definition of a man.

http://www.ancientfacts.net/about/greek-philosophers/