"According to Diogenes Laërtius’ third-century Lives and Opinions of the Eminent Philosophers, Plato was applauded for his definition of man as a featherless biped, so Diogenes the Cynic “plucked the feathers from a cock, brought it to Plato’s school, and said, ‘Here is Plato’s man.’” Source: https://www.laphamsquarterly.org/animals/miscellany/plato-and-diogenes-debate-featherless-bipeds