In 'Amphitryon', a comedy by the Roman playwright Plautus, the god Mercury takes on the appearance of Sosia, Amphitryon's slave, to help Jupiter seduce his master's wife. The real Sosia comes face to face with himself and ends up doubting his own identity. Molière revived the plot to great success in 1668, and the hapless servant's name became 'sosie', the French word for a perfect double.
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.