Okay, I talked to our resident biochemist. According to him most enzymatic activity will continue in the cell for quite a while after an animal dies. Lack of oxygen/excess of nitrogen has no effect on these metabolic mechanisms. However, the lack of blood flow means cellular waste products aren't removed nor are fresh nutrients and chemicals moved to the cells. The interior of the cells becomes very acidic which leads to the breakdown of cell walls.

Meanwhile, anaerobic bacteria are multiplying out of control. Normally they are kept in check by your immune system as well as...defecation. Half the dry mass of stool is usually bacteria. Since the animal isn't defecating the bacteria remains inside the body to multiple and "eat" the surrounding flesh. Cells rupturing due to increased acidity flood the anaerobic bacteria with more food. These bacteria are also producing waste products and gases.

The only way to really prevent this is by removing most of the water from the carcass. Without water everything grinds to a halt.

-Blast