This hour, we dive into the messy mystery in the middle of us. What's going on down there? And what can the rumblings deep in our bellies tell us about ourselves?

We stick our hand in a cow stomach, get a window into our core (thanks to a hunter who became a walking science experiment in the 1800s), and listen in on the surprising back-and-forth between our gut and our brain. And we talk to a man who kind of went out of his mind when a medical procedure left him (for a little while) gutless.

Correction: An earlier version of this piece implied that subjects in the human probiotics study were given a larger dose of probiotics than they actually were. We also compared the results of the study to the effect of giving people anti-anxiety medication. The subjects did experience a significant positive mood change, but the researchers did not compare that result to the effect of anti-anxiety medication. The audio has been adjusted to reflect these facts.