How horses whinny has long been a mystery. The sound is quite distinct from any other in the animal kingdom. And now scientists think they’ve discovered why: horses whinny by producing sounds at two frequencies at the same time—much like singing and whistling simultaneously.The findings, which were published on Monday in Current Biology, suggest horses produce sounds at two frequencies in two distinct ways in their larynx, or voice box. A low-frequency sound of about 200 hertz is produced by vibrating the vocal cords, just as we do while singing. And a high-frequency sound of more than 1,000 hertz is produced by whistling within the larynx.
In general, the larger an animal—and its larynx—is, the lower the frequency of sound it produces. Meanwhile smaller critters, such as mice, produce high-frequency whistles. But this study suggests that horses are unique in their ability to whistle and vibrate their vocal cords at the same time, the authors write.