His machine uses Skinnerian training. He put coins and peanuts around the machine. The crows eat the peanut on the feeder tray. Then Joshua took away the nuts and left coins in the feeder tray. It pisses off the crows. They sweep the coins around with their beaks, looking for food. When a coin accidentally drops into the slot, it dispenses a peanut. Next, Joshua took away the coins. The crows learned to find coins elsewhere and deposit them.