In 1980, primatologists in Kenya played back recordings of vervet alarm calls. 'Leopard' call: the monkeys climb trees. 'Eagle' call: they look up and dive into bushes. 'Snake' call: they stand up and scan the ground. These signals point to specific categories, yet they still don't add up to a language.
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.