Risus sardonicus

L. risus = smile and L. sardonicus = diabolic

Risus sardonicus refers to the highly pathogmonical persisting muscle spasms, producing the “diabolical grin” found in patients affected by tetanus, strychnine poisoning or Morbus Wilson.

Hong Kong: Unvaccinated woman develops tetanus - Outbreak News Today
Risus sardonicus in a tetanus patient