Contrary to popular belief, sign language isn't universal. Ethnologue lists around 150 and the World Federation of the Deaf estimates more than 300, each with its own vocabulary and grammar. Deaf people in London and New York don't sign the same language, even though their hearing neighbours all speak English.
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.