A liquid concoction, often laced with toxic chemicals, is a central villain in the controversy over extracting natural gas by fracturing rock beneath the earth’s surface. Opponents fear this fracking fluid may foul water supplies, endangering human health and the environment. Adapting, the industry is responding to public concern. Giant energy services company Halliburton, in a safety demonstration at an August 3 industry conference in Colorado, had an employee demonstrate just how palatable fracking fluid can be. He drank it.