Rigor mortis can take between three to six hours to set in after the death of a cat, according to Rest in Pets. The condition, which is part of the decomposition process, is a natural occurrence after the death of an animal.
Rigor mortis creates stiffness in a cat’s muscles hours after it dies, and can last from 12 hours to several days. Rigor mortis and decomposition do not occur immediately following a cat’s death. It is accelerated or decelerated by environmental conditions. For example, Living With Pet Bereavement points out that if temperatures are warm, rigor mortis begins sooner than if temperatures are cooler. Rigor mortis also occurs more quickly with smaller cats than with larger ones.