The sounds in 'think' and 'this', made with the tongue between the teeth, are much less common than English speakers might assume. In a sample of 567 languages from the World Atlas of Language Structures (WALS), they appear in only about forty, fewer than one in ten. French, German and Mandarin all lack them, hence 'ze' and 'zis'. Castilian Spanish, Greek and Classical Arabic do have them.
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.