Rigor mortis, or a stiffening of the body, sets in about two to six hours after death [source: Marchant, Middleton]. While the body as a whole may be dead, little things within the body are still alive. Skin cells, for example, can be viably harvested for up to 24 hours after death [source: Mims]. But some things that are still alive lead to the putrefaction, or decomposition, of the body -- we're talking about little organisms that live in the intestines.