Here is a very basic design. I am trying to use the Line Width tool to fill in the right side of the mouth. Only it is not working. No matter what I do -it won't fill it in. I circled some of the key indicators in red.
There's a rule about eyebrows (if you're into traditional drawing style) which say that the horizontal middle construction line of an eye and its eyebrow should have the same origin. There's an illustration about this in "Illusion of Life".
Yes, I'm aware of the tabby markings (I have bred Abyssinian cats for some time), but I'm also aware that cats do have eyebrows. You can clearly see them in the picture, between the eyes and the upper vibrissae (whiskers). You can also feel them if you have a cat. It is a row of hairs that runs distinctively in another direction than the surrounding hairs, and are also a little bit coarser than the other hairs in the coat.
Just as human eyebrows, they are meant to protect the eyes from small objects entering the eyes from above. I guess that is the reason we humans still have eyebrows.