Beyond babies, and brains, the coupling of hand and mouth can also be observed in everyday behaviours. Darwin noted that ‘children learning to write often twist about their tongues as their fingers move, in a ridiculous fashion’. Work since has documented tongue protrusions in a wide range of activities, not just during writing and not just in kids. The US basketball star Michael Jordan was known for sticking out his tongue while dribbling or dunking the ball. Watch someone thread a needle or unlock their smartphone, and you might see the same. These ‘ridiculous’ behaviours are just one type of what are called ‘hand-mouth sympathies’. A more subtle type occurs when people use their hands while simultaneously producing a vocalisation. One-year-olds, for instance, vocalise differently when they grasp a small object versus large object.
Interesting!