The human mouth is relatively small compared to other primates and can be openedand closed rapidly. It is also part of an extended vocal tract that has much more of anL-shape than the fairly straight path from front to back in other mammals. In contrastto the fairly thin flat tongue of other large primates, humans have a shorter, thickerand more muscular tongue that can be used to shape a wide variety of sounds insidethe oral cavity. In addition, unlike other primates, humans can close off the airwaythrough the nose to create more air pressure in the mouth. The overall effect of thesesmall differences taken together is a face with more intricate muscle interlacing in thelips and mouth, capable of a wider range of shapes and a more rapid and powerfuldelivery of sounds produced through these different shapes.