The snakes are copperhead (or radiated) ratsnakes, and he has the head of one in his mouth. These snakes can be quite aggressive, and I saw a couple of other (accidental) bites elsewhere during my trip, both from this species.
The audience were fascinated. But this isn't educational, I personally can't see how it's entertaining, it's very dangerous, distressing for the snakes, and clearly this act is taking its toll on the guy's forearm.
What a stupid act, nothing good for the snake, nothing good for the human and the audience take nothing away other than seeing a man getting bitten and abusing reptiles!