Spoken by roughly 250 to 380 people along the Maici River in the Brazilian Amazon, Piraha is the last surviving member of the Mura language family and one of the most debated languages in modern linguistics. It has one of the smallest sound inventories in the world, between 10 and 13 phonemes, can be hummed or whistled, and has no words for exact numbers.

This episode explores the language's phonetics, including a double-flap consonant used only among close acquaintances and different pronunciations for men and women; its evidentiality suffixes that force speakers to state how they know something; Michael Frank's spool-matching experiment; Daniel Everett's eight months of failed math lessons; and the fight over recursion that pitted Everett against defenders of Noam Chomsky's universal grammar.

• How pitch and rhythm carry meaning  ...