''Risus sardonicus'' or rictus grin is a highly characteristic, abnormal, sustained

spasm A spasm is a sudden involuntary contraction of a muscle, a group of muscles, or a hollow organ, such as the bladder. A spasmodic muscle contraction may be caused by many medical conditions, including dystonia. Most commonly, it is a musc ...

of the

facial muscles The facial muscles are a group of striated skeletal muscles supplied by the facial nerve (cranial nerve VII) that, among other things, control facial expression. These muscles are also called mimetic muscles. They are only found in mammals, alth ...

that appears to produce grinning. It may be caused by

tetanus Tetanus (), also known as lockjaw, is a bacterial infection caused by ''Clostridium tetani'' and characterized by muscle spasms. In the most common type, the spasms begin in the jaw and then progress to the rest of the body. Each spasm usually l ...

strychnine poisoning Strychnine poisoning is poisoning induced by strychnine. It can be fatal to humans and other animals and can occur by inhalation, swallowing or absorption through eyes or mouth. It produces some of the most dramatic and painful symptoms of any kno ...

, or

Wilson's disease Wilson's disease (also called hepatolenticular degeneration) is a genetic disorder characterized by the excess build-up of copper in the body. Symptoms are typically related to the brain and liver. Liver-related symptoms include vomiting, wea ...

, and has been reported after

execution by hanging Hanging is killing a person by suspending them from the neck with a noose or ligature strangulation, ligature. Hanging has been a standard method of capital punishment since the Middle Ages, and has been the primary execution method in numerou ...

. The condition's name derives from the appearance of raised eyebrows and an open "grin", which can appear sardonic or malevolent to the lay observer, displayed by those experiencing these muscle spasms.

Causes

It is most often observed as a sign of tetanus. It can also be caused by poisoning with strychnine or Wilson's disease. In 2009, scientists at the

University of Eastern Piedmont The University of Eastern Piedmont "Amedeo Avogadro" (; shortened to UNIPMN or UPO) is a university located in Alessandria, Novara and Vercelli, in the region of Piedmont, Italy. It was founded in 1998 and is organized in seven faculties, which ...

wrote that they had identified hemlock water-dropwort (''

Oenanthe crocata ''Oenanthe crocata'', hemlock water-dropwort (sometimes known as dead man's fingers) is a flowering plant in the Apiaceae, carrot family, native to Europe, North Africa and western Asia. It grows in damp grassland and wet woodland, often along ri ...

'') as the plant historically responsible for producing the sardonic grin. This plant is the most likely candidate for the "sardonic herb", which was a

neurotoxic Neurotoxicity is a form of toxicity in which a biological, chemical, or physical agent produces an adverse effect on the structure or function of the central and/or peripheral nervous system. It occurs when exposure to a substance – specifical ...

plant used perhaps for the ritual killing of elderly people in pre-Roman Nuragic Sardinia.

References

{{Reflist Facial expressions Laughter Tetanus Strychnine poisoning

Causes

See also

References