What is rigor mortis? Well, within only a few hours of the death of a being, the body of the person or the animal will get stiff and it will lock in place. This natural phenomenon is what is called rigor mortis or the technical term of postmortem rigidity. Medically speaking, the term of rigor mortis is defined as body muscles temporary becoming rigid shortly after death. Rigor mortis happens because of some biochemical changes that happen in muscle tissue, the formation of an enzyme that is called Adenosine troposphere or ATP for short stops after death because of a lack of oxygen to the body. Since ATP helps to provide energy for muscle movement, this stoppage in the production of this enzyme results in proteins like myosin molecules sticking to the body muscle’s actin filaments, this causes a contraction and also the stiffening of the muscle tissue. READ MORE!