Imagine if you had an extra organ with 10 times as many cells as the rest of your body, and that organ affected everything from your digestion to your mood. It turns out you do have something like that, and it's made up of all the tiny life forms that live in your body's nooks and crannies.

Originally released by Inside Science, 2018. Streaming video file encoded with permission for digital streaming by Infobase on January 03, 2019.

American Gut Project (2:21);