Where does crocodile tears' come from?

If someone is crying in an attempt to fake remorse or empathy, we say they are shedding “crocodile tears.” But how and why did we start pegging insincere displays of emotion to the toothy reptiles?

The origin may have become popular around the 14th century when a bestselling memoir, The Voyage and Travel of Sir John Mandeville, referenced serpents who sob while eating their human victims:

And in the night they dwell in the water, and on the day upon the land, in rocks and in caves. And they eat no meat in all the winter, but they lie as in a dream, as do the serpents. These serpents slay men, and they eat them weeping; and when they eat they move the over jaw, and not the nether jaw, and they have no tongue. In the centuries since, crying crocodiles have become a metaphor for superficial remorse. The expression has been used as a fable to teach sincere repentance, by Shakespeare to convey false grief, and, more recently, by media mocking tearful politicians or murder suspects.

In 2007, University of Florida zoologist Kent Vliet actually proved that the animals do sob while snacking. Vliet's theory is that when the animals enthusiastically smack their jaws, the movement forces air through the crocodiles’ sinuses and ultimately empties tears into their eyes. Their eyes not only water but can froth and bubble, as Vliet witnessed at the alligator park, where some even teared up in anticipation of their meal of chicks, quail, and feed biscuits.
Source: www.mentalfloss.com