The key to learning the language is the tribe’s singing, Keren said: the way that the group can drop consonants and vowels altogether and communicate purely by variations in pitch, stress, and rhythm—what linguists call “prosody.” I was reminded of an evening in the village when I had heard someone singing a clutch of haunting notes on a rising, then falling scale. The voice repeated the pattern over and over, without variation, for more than half an hour. I crept up to the edge of one of the Pirahã huts and saw that it was a woman, winding raw cotton onto a spool, and intoning this extraordinary series of notes that sounded like a muted horn. A toddler played at her feet. I asked Everett about this, and he said something vague about how tribe members “sing their dreams.” But when I described the scene to Keren she grew animated and explained that this is how the Pirahã teach their children to speak. The toddler was absorbing the lesson in prosody through endless repetition—an example, one might argue, of Edward Sapir’s cultural theory of language acquisition at work.