"For many animals, alarm calls are more than simple squawks of fear. Vervet monkeys, for instance, use different sounds to warn of different types of predator. "Leopard!" is not the same as "snake!" or "eagle!" If you hide a loudspeaker in the bushes, and startle unsuspecting monkeys by playing recordings of "snake!" at them, they will look around at the ground. "Eagle!" makes them look up. "Leopard!" sends them scampering to the trees."