It's called a ruminant stomach and is divided into four compartments:
* Rumen: The largest compartment, where food is initially fermented by bacteria.
* Reticulum: Where food is further broken down and sorted.
* Omasum: Absorbs water and nutrients.
* Abomasum: The "true" stomach, where digestive juices break down food.
This complex system allows deer to digest tough plant material efficiently, making them very adaptable herbivores.