Acoustic signals are noises that animals produce in response to a specific stimulus or situation, and that have a specific meaning. These may be vocal communications emitted from the animal's larynx, such as a wolf's howl; sounds produced by appendages, such as a cricket's chirp; or sounds created by an animal's interaction with its environment, such as a rabbit thumping the ground with its hind foot when it sights danger. The physiological characteristics of animals, such as throat shape or lung size, create constraints on the type of acoustic signals an animal produces. Similarly, the anatomical properties of the ear, and the processing capabilities of the auditory regions of the brain, can limit the range of sound that a species is capable of detecting. Compared with most mammals, humans have an abnormally complex system of vocalization that is supported by the expanded language centers of the...