rigor mortis

In Latin, rigor means "stiffness" and mortis means "of death." The term refers to the hardening of muscles after death, which is caused by chemical changes that start immediately after death. This rigidity of the tissues sets in just 2-4 hours after death in humans (longer in other animals), peaks after about 24 hours, and then dissipates gradually until it disappears completely after anywhere between 1-6 days.