What is the explanation behind the sensitive awareness showed by elephants within their own particular tribes? Katy Payne tells how, on one occasion, a group of elephants she was observing appeared restless. They looked around them, as if searching for someone missing. Then, after a while, from over the horizon, an elephant lumbered into view. Once he arrived, the whole group calmed down, and then, amicably set off for a waterhole together. Payne discovered, through the use of high-frequency recorders, that elephants emit sounds that humans cannot hear. By her account, at least 50 sq/km can be filled by an elephant call. She also discovered that an elephant's delicate perception can detect calls with different meanings. Her extremely well-written book ends with an appeal for the conservation of elephants, whose numbers are falling.