Decomposition Stages:

Fresh. One to two days. Minimal visual signs like livor mortis, rigor mortis, and minor changes to skin color as blood pools. Algor mortis, the cooling of the body occurs. Initial insect arrival occurs. Internally, enzymes begin breaking down tissue, and bacteria spread while assisting.

Bloat. Two days to a week. Gases build up internally. Eyes and tongue may protrude. Skin will take on a distinctive marbled look. The smell of death, caused mostly by the chemicals Cadaverine and Putrescine, which smell like rotting flesh will begin to be detected. Other chemicals may contribute. Skatole, which has a strong feces odor. Indole has a mustier, mothball-like smell. Hydrogen sulfide smells like rotten eggs. Methanethiol smells of rotting cabbage. Dimethyl disulfide and trisulfide have a foul, garlic-like odor.

Decay. Five days to two weeks. Gases will begin to vent, deflating the corpse. Fluids begin to escape from orifices. Insect activity is high, and multiple species will be present. Internal organs break down in a relatively predictable order.

Post decay. 10 days to three weeks. Soft tissue is broken down or eaten. The body progresses to a state where most of the soft tissue is gone, but what remains will still be breaking down and wet.

Dry, or skeletonization. Two weeks +. The remaining tissues, primarily tendons, some cartilage, and any connective tissues otherwise protected by position or prevention of exposure will be dry and odorless.

Decomposition rate is determined by a combination of temperature, humidity, insect access, and any mitigating factors like clothing. Cold and low humidity decrease the rate, while higher ranges accelerate it.

The smell of decomposition is distinct. But it is also difficult to describe. Sickly sweet is one common phrase, but falls woefully short.