Squash and stretch is very important in facial animation, not only for
showing the flexibility of the flesh and muscle, but also for showing the
relationship of between the parts of the face. When a face smiles broadly,
the comers of the mouth push up into the cheeks. The cheeks squash and
push up into the eyes, making the eyes squint, which brings down the
eyebrows and stretches the forehead. When the face adopts a surprised
expression, the mouth opens, stretching down the cheeks. The wide open
eyes push the eyebrows up, squashing and wrinkling the forehead.