Stomachs growl because of the physiological processes involved in digesting food and pushing it through the intestinal tract. The stomach is an incredibly muscular organ which frequently contracts itself to help circulate digestive juices. When your stomach is empty, these juices slosh around with the gases generated during the process of digestion, generating a distinctive growling noise; the noise is also caused by the walls of the stomach coming into contact with each other.

The issue of growling stomachs was of such interest to the Greeks that they developed a word to describe it: borborygmi, which means “growlings.” You may occasionally hear doctors talking about borborygmi as a more polite term for growling stomachs. As a general rule, borborygmi is not a cause for concern, because it is simply part of the natural digestive process. Stomachs growl because the stomach never fully ceases its digestive work; in fact, digestive juices continue to work even after death.

Intestines also growl, although you may not hear it, because the soft tissue of your body muffles the sound from the outside. Growling in the intestines is also caused by digestive processes, as your body slowly pushes food and waste material to its eventual end destination. If you have a human or animal stomach handy, you can listen for the sounds of growling in the stomach and intestines; you may find it a bit hard to put your own head close enough to your stomach to hear your intestines growl.

Often, stomachs growl when people are hungry, because their stomachs are empty. However, a growling stomach does not necessarily mean that someone is hungry, it just means that the stomach is empty or relatively empty. For example, stomachs growl in the middle of the night a lot as they process the food people have eaten during the day, but people don't realize this, because they are asleep.

There are some situations in which borborygmi is a sign of a health problem. People with irritable bowel disease, for example, often experience frequently growling stomachs along with a host of unpleasant symptoms including cramps. If your stomach growls a lot, or you experience extreme cramping or other gastrointestinal symptoms like diarrhea, you may want to see a doctor to make sure that everything is well with your digestive system.

Just think of the stomach as a carton of juice; if you shake a full carton of juice, you hear minimal sounds, whereas a carton which is almost empty will be quite noisy. The next time you hear stomachs growl, you can write it off as a simple case of borborygmi caused by the amazingly efficient and powerful digestive system.