The saying derives from an ancient belief according to which the crocodiles would shed tears of repentance after feeding on their prey. In popular culture, this saying refers to a person who first commits a bad deed on purpose, then pretends to feel remorse.
In reality, the crocodiles "cry" for physiological reasons, that is to lubricate and clean up the eyeball in order to facilitate the movement of the second eyelid, used during the permanence in water. Furthermore, through tears, the crocodile expels the salts that accumulate in the body.
