A horse's whinny is an unusually distinctive mix of sounds including both high and low frequencies. Reporting in Current Biology, researchers demonstrate how horses produce high-frequency sounds that defy their large size while simultaneously producing lower tones: they whistle through their larynx while vibrating their vocal folds as a human does while singing. Horses likely evolved these vocalizations to be able to convey multiple messages to one another at the same time, says the team.