The most important aspect of an expressive animal portrait are the eyes. They put expression into the illustration, so it is very important to work the portrayed eyes out. Eyes are never unicoloured. Even if some eyes are very dark, you can always see a little bit of light in the eyes of an animal. There are highlights as a reflex towards the source of light and a progression of brightness on the surface of the iris. Especially placental mammals show facial expressions. The position of the eyelids plays an important role as well.