Crocodiles intentionally eat stones or rocks and for years it was thought they might help a crocodile stay under the water longer and dive deeper. Since crocodiles like to ambush their prey by floating in water with only their eyes and nostrils showing, perhaps having rocks in their stomach helps keep their bodies under water, out of sight.
More recently scientists have questioned this hypothesis and while there may be some incidental truth to the diving deeper theory, we do know rocks in the digestive system of some animals help digestion. These rocks are called gastroliths (literally, “stomach stones”) and they can sometimes stay inside an animal’s stomach for years. Since crocodiles often swallow their prey whole, rocks in a crocodile’s stomach may well help their digestive system crush and grind their meals, particularly when they consist of animals with shells and tough bones!