The human mouth is relatively small compared to other primates and can be opened
and closed rapidly.
In contrast
to the fairly thin flat tongue of other large primates, humans have a shorter, thicker
and more muscular tongue that can be used to shape a wide variety of sounds inside
the oral cavity. In addition, unlike other primates, humans can close off the airway
through the nose to create more air pressure in the mouth. The overall effect of these
small differences taken together is a face with more intricate muscle interlacing in the
lips and mouth, capable of a wider range of shapes and a more rapid and powerful
delivery of sounds produced through these different shapes.