Go With Your Gut

In the wake of the Chertoff gut-trusting scandal, Slate's Explainer asks: "How much does your gut actually know?"

Plenty. In fact, your gut is so packed with neurons that in the 1990s one gastroneurologist, Michael Gershon, dubbed it the "second brain." This enteric nervous system looks a lot like the network of cells that exists in your actual brain, and it uses all the same neurotransmitters (including 95 percent of the body's serotonin). It can operate on its own—that's without cranial consultation—to start or stop the flow of digestive enzymes, regulate pH levels inside the gut, or expel that week-old sushi that you ate against the better judgment of brain No. 1.

President Bush told Washington Post reporter Bob Woodward that he was a "gut player," when explaining his decision to go into Iraq. No word on the relationship between the wattage of brain No. 1 and brain No. 2.