The ability to strongly focus the eyes is a characteristic of strong Yin development.
An added bonus from this picture is that it provides the opportunity to compare strong and weak Yin development, because the man has a weakly developed Yin part of the body.
The observations that lead to that conclusion include his entire body leaning to the left,
his head is slightly rotated to the right causing it to be misaligned with the center of the body,
and the fact that the base of his tongue protrudes out of his mouth at an angle that approximately matches the angle of his head,
while the tip of the tongue points off at a completely different angle to his right.
In contrast the woman with strong Yin development has a body that is straight up and down,
and her head is aligned with the center of her body.
