On La Gomera in the Canary Islands, a neighbor two miles away as the crow flies can be a three-hour hike down and up a volcanic ravine. The islanders' answer was Silbo Gomero, a whistled register of Spanish that carries up to five kilometers. This episode explains the mechanics: a knuckle anchors the tongue, the vocal cords fall silent, and speech is compressed into a single whistle between 1,000 and 3,000 hertz that cuts through wind, leaves, and surf, with consonants expressed by breaking, rising, or falling pitch.

The episode traces the system from the indigenous Guanches, who whistled long before the Spanish arrived, through the Spanish vocabulary grafted onto that ancient medium, to the near-death of Silbo in the mid-20th century when emigration, the telephone, and the stigma of peasant farming drove it underground. It covers the late- ...