Physical Changes
Seven hours after death, the body begins to experience physical changes. The skin becomes cool and pale, and blood pools in the lowest portions of the body. Rigor mortis, the stiffening of the body, usually sets in within three to four hours of death and can last for several days. During this time, the body becomes increasingly stiff, until it is completely rigid.
Autolysis
Seven hours after death, the body begins the process of autolysis, also known as self-digestion. This process occurs when the body’s cells produce enzymes that break down the cells and tissues. The enzymes are released from the cells by apoptosis, a kind of programmed cell death. Autolysis is believed to be one of the main causes of the strong odor associated with a dead body.
Decomposition
Decomposition, the process of breaking down the body’s tissues, begins to take place within 24 hours of death. Bacteria within the body begin to break down the body’s cells and release gases such as hydrogen sulfide, methane, and cadaverine, which produce the characteristic odor of a dead body. As the body continues to decompose, insects such as flies and beetles will begin to feed on the tissues. This process is known as insect colonization.