there is scarcely a feature of the human body that has not, at one time or another, been advocated as an index of certain faculties, and now it is the turn of the external ear. Although not one of ...

A dog training whistle makes sound waves that have a frequency of 40,000 Hz. Dogs ears can detect the sound, humans can’t because the frequency is above 20 kHz. In 2005, Howard Stapleton from ...