Rigor Mortis is the stiffening and contraction of the muscles due to chemical reactions that take place within the muscle cells after death. It typically follows a pattern, first in the small muscles...
They don't. It occurs over the first 36 hours after death. Immediately after death the body is limp. With time it becomes increasingly rigid due to lack of ATP and build up of lactic acid.
My guinea pig died on my bed where he was resting and afterwards I petted him for an hour. When I finally had the heart to put him in the little box he was already stiffening. I was surprised how...