This article is about the sign of death. For other uses, see Rigor mortis (disambiguation) . Rigor mortis (Latin: rigor stiffness, mortis of death) is one of the recognizable signs of death, caused by chemical changes in the muscles after death, causing the limbs of the corpse to stiffen.t the time of death, a condition called primary flaccidity occurs. Following this, the muscles stiffen in rigor mortis. All muscles in the body are affected. Starting between two to six hours following death, rigor mortis begins with the eyelids, neck, and jaw.