In Old French, the plural of 'cheval', horse, was 'chevals', then 'chevaus' once the l had turned into a u sound. Medieval scribes abbreviated the ending '-us' with a sign that looked like an x, giving 'chevax'. That sign was eventually read as a real letter, and the u was put back in front of it. The result, 'chevaux', effectively contains the u twice.
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.