Once animals die, the circulation system stops working and cells are no longer being delivered the blood or oxygen they need. At this point the cells dont have the energy necessary to maintain their biochemistry, so ions start to leak through the membranes and systems began to break down resulting in the cells death. Cell and tissue materials begin to be decomposed and broken into proteins and amino acids through a combination of bacteria (either from inside the body - like in our intestines or from the outside world) and the bodys own internal enzymes. The bacteria and enzymes will ultimately completely digest the tissue, but other scavengers or insects may also play a role in breaking those materials down.

Generally other organisms consume them. In anaerobic environment, tissues oxidize, and in ananaerobic environment, the fermenters and sulfideoxidizers move in.

The proteins that hold them together get digested, either by bacteria or by other things.

Typically, animals are decomposed by bacteria and othermicroorganisms. These other critters, further down the food chain,rely on dead animals as a food source.

Cellular tissues can be broken down by endogenous (meaning from within the creature itself) proteases. Proteases are enzymes (proteins) that can attack and degrade other proteins into smaller molecules, such as methane (CH₄), Ethanol, water, and other smaller features. Also,bacteria and other microbia participate in the breakdown of cellular tissues.