“The gorilla is the only primate to have discovered a nonvocal sound mechanism: it drums on its chest with its fist, producing a loud, hollow sound. This is done both when making vocal sounds and on its own. The gorilla has discovered the property of resonance, independent of the natural mechanism of the voice box. It seems forever on the verge of discovering the musical instrument without being able to make the transition from personal to artificial sound. So far as we know only man has done this.”