In American Sign Language, as in many others, the face does more than show emotion: it carries grammar. Raised eyebrows turn a statement into a yes-or-no question. Furrowed brows go with open questions such as 'who?' or 'where?'. The mouth can act like an adverb, showing that something is done with ease or carelessly. Signing with a blank face is a bit like writing without punctuation.
In Kuşköy, a mountain village in northern Turkey, people talk across valleys by whistling Turkish. A 2015 study showed that whistled Turkish draws on both hemispheres fairly evenly, whereas spoken Turkish relies mostly on the left. The physical form of the signal, it turns out, matters to the brain.
Speech has no gaps between words. In 1996, researchers played 8-month-old babies a continuous stream of made-up syllables for just two minutes. The infants picked out the 'words' by tracking which syllables tend to follow one another. That's probability calculation, done without a calculator or any visible effort.