A horse's neigh may be unique in the animal kingdom. Now scientists know how they do it

A horse's signature whinny comes from a combination of whistling and singing

NEW YORK -- NEW YORK (AP) — Horses whinny to find new friends, greet old ones and celebrate happy moments like feeding time.

How exactly horses produce that distinctive sound — also called a neigh — has long eluded scientists.

The whinny is an unusual combination of both high and low pitched sounds, like a cross between a grunt and a squeal — that come out at the same time.

The low-pitched part wasn't much of a mystery. It comes from air passing over bands of tissue in the voice box that make noise when they vibrate. It's a technique similar to how humans speak and sing.

But the high-pitched piece is more puzzling. With some exceptions, larger animals have larger vocal systems and typically make lower sounds. So how do horses do it?