Our brain is divided in two hemispheres, the right one for emotions and the left one for reflection. But each hemisphere control the opposite half of our body (left hand is controled by right hemisphere). Therefore the left part of our face is emotion, and the right one is reflection.
I applied this principe in this picture. This face has black reflection, and white emotion: it seems to have dark logic, but is happy.
Now, take a look at the eyes... They are of the opposite color of the face! Since eyes are the reflect of the soul, we can guess that this guy has in reality a right logic, but dark feelings. Eyes can not lie, so this face is a mask.