Physical Changes
Within an hour after death, the body begins to undergo physical changes. The skin becomes pale and cool to the touch. Rigor mortis, or stiffening of the joints and muscles, begins to set in. The eyes may remain open, or may close. The body may become rigid, and the face may become distorted.
Internal Changes
Internally, the cells start to break down as the body begins to cool. This breakdown of cells leads to the release of chemicals and enzymes that contribute to the odor associated with a decomposing body. As the body cools, the lungs may fill with fluid, making a rattling sound.
Chemical Changes
As the body begins to decompose, bacteria and other microorganisms break down the body's tissues. This process leads to the release of gases such as ammonia, methane, and hydrogen sulfide, which contribute to the odors associated with a decomposing body.
Environmental Changes
As the body begins to decompose, it can attract scavengers such as insects, small animals, and birds. These creatures may feed on the decomposing body, further breaking it down and leading to the release of more chemicals and odors.