Stages of decomposition
Early Stage:
Autolysis - self digestion. Cells continue metabolizing after the death. One of the byproducts of metabolism is CO2. Usually removed by cells by circulation & respiration, but if those cease after death, CO2 builds up inside cells. CO2 is acidic. Lysosome is an organelle inside the cell is surrounded by a single membrane. Because the cell is becoming acidic, the lysosome is among the first structure to break down, and the enzymes inside it begin digesting the cell from the inside out. This is autolysis.
Interior of cell liquified is nutrient-rich. Surface of the skin becomes loose and sloughs off the body. The nutrient rich fluids give the body a moist appearance. This allows second major decomp stage to begin.