The Pirahã, a few hundred people living along the Maici River in Brazil, have no word for 'one', 'two' or 'three'. The terms long translated that way actually express relative amounts: 'few', 'a bit more', 'many'. In 2008, a study in Cognition found they could easily match rows of objects in plain sight, but erred as soon as they had to remember an exact quantity. The authors call number words a 'cognitive technology'.
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.