The human body plays host to a huge range of tiny organisms, mostly bacteria and some fungi, that live symbiotically within us. These microbes, many of which we even share with our dogs, are 10 times more plentiful in the human body than actual human cells. This NPR animation from artist Ben Arthur and correspondent Rob Stein, “The Invisible Universe,” explores the vast world of microorganisms that live all throughout our bodies.

“We still have a lot to learn about what many of our microbes are really doing,” as Stein says in the video. We’re just starting to understand how these microbes affect our health, especially in the gut, where scientists have recently begun experimenting with implanting microbe cocktails into patients to fight off infections—you know, fecal transplants.