Risus sardonicus (sometimes called sardonic smile) is a highly characteristic, abnormal, sustained spasm of the facial muscles that appears to produce grinning.
The name of the condition derives from the appearance of raised eyebrows and an open "grin" - which can appear malevolent to the lay observer - displayed by those suffering from these muscle spasms.
In 2009 scientists at the University of Eastern Piedmont in Italy claimed to have identified hemlock water dropwort (Oenanthe crocata) as the plant responsible for producing the sardonic grin. This plant is the most-likely candidate for the "sardonic herb," which was a neurotoxic plant used for the ritual killing of elderly people in pre-Roman Sardinia.
In popular culture
The condition was the inspiration behind the 1981 track Sardonicus by UB40, on their album, Present Arms. The song has strong political linkages with false smiles.
Arthur Conan Doyle's hero Sherlock Holmes uses the term to describe the facial distortion of the murder victim Bartholomew Sholto in his story The Sign of the Four.
Risus Sardonicus is also known as the Hippocratic Smile
In various Batman comics The Joker often kills his victims with toxins that induce Risus Sardonicus.