WHY? is our attempt to answer all the questions every little kid asks. Do you have a question? Send it to why@mentalfloss.com.

Farts can make a lot of different noises. Some farts are high and squeaky. Some explode like a machine gun. Some don’t make any noise at all. It all depends on how much gas you have in your intestines and on the muscles around the anus (the opening in your butt).

Farts happen when your body lets out gases. Some of that gas comes from air that you swallow as you are eating and breathing. Some of it is made as your body digests, or breaks down, food to turn it into energy. Millions of tiny organisms called bacteria living in your gut help with digestion too. As they do, different gases get released. Those gases move along through your large intestine until they reach its end, called the rectum. Then they come out as farts: some quiet, some loud enough to rattle the windows!

The sound of your farts is affected by how much gas has built up inside, and how fast it comes out. It also depends on how tight the sphincter (SFINK-ter) muscles are. They ring the anus and help keep it closed. All these things together cause vibrations as the gas pushes through. If the sphincter is relaxed, your fart will probably be on the quieter side—pffft! But if those muscles are tightened up (as they are when you are trying not to fart), you’re probably going to squeak, toot, rumble, or roar. 

To learn more about gut bacteria, farts, and sharing poop for health reasons, watch this video from MIT.