Rodents, rabbits and even some apes eat their own dung to absorb maximum nutrition from their meals
Plant material is difficult to digest, and when it leaves the body it is still full of material that hasn’t been broken down fully.
It’s extremely similar to how a cow regurgitates its food to chew it more, but rodent digestive systems are far less sophisticated.
Dogs also consume their own leavings, much to the disgust of their owners. Their dung contains vitamins left by the bacteria in the dog’s intestines that can’t be absorbed through the intestinal wall. Eating the faeces allows the vitamins to be absorbed through the stomach, along with any undigested protein the poo contains.