The horse whinny, or neigh, has been a familiar sound at least since the animal was domesticated, around 4,200 years ago. But until now, scientists didn't understand how horses produced this characteristic vocalization. New research shows that horses (Equus ferus caballus) whinny by making two distinct sounds at once: a low-frequency 'nickering' sound made in their vocal folds, combined with a high-pitched whistle produced by forcing air through the cartilage of their larynx. The biomechanics of this dual-frequency sound, or biphonation, are described on 23 February in Current Biology1. The authors theorize that this multilayered vocalization enables the animals to convey complex messages to each other. The animals' ability to whistle while vocalizing earns them membership into a small club of creatures that can make biphonic sounds, which includes several birds species, human beat boxers, Mongolian throat singers, and those who can sing while whistling. Of all the noises horses...
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