The start of the digestive system is in the mouth then it goes down your esophagus then your stomach then the small intestine and then the large intestine and then the food comes out of your body then into the toilet. If we did not have teeth it would be very hard to eat because the teeth crunch the food up and then we can swallow it if we did not have teeth our bodies would have a very bad time swallowing the food, birds don't have teeth so some of them eat stone then it goes in a part of it's esophagus and then the rocks go in and when it eats the stones rub the food so they can digest it probably and that is why sometimes you can see some birds eat rocks it is not easy to find birds doing that because birds usually go away when you are there.