Crocs eat rocks to help in digestion and to add weigh so that they can stay submerged underwater. (Crocodiles can stay submerged for as long as an hour.) On average, a crocodile contains 10 to 15 pounds of stone in its stomach. The stones must fill them up, because crocodiles really don't eat that much and not very often either. Because they are slow-moving and cold blooded, they can survive on about the same amount of food as a bird.