The rumen is the organ that ruminants have that allows them to digest course cellulose materials such as grasses and shrubs. It is a fermentation container that provides an anaerobic environment, constant temperature and pH, and good mixing. Some nutrients are absorbed by the rumen while others flow downstream for absorption by the stomach and intenstines.

Cougars leave the rumen intact when they feed at a carcass while wolves tear it to shreads. This intact rumen along with nearby tracks indicate that this elk was killed and eaten by a cougar.

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