A rock pile that still has to have a face.
Every plate is a decision about where the expression lives. Get the brow wrong and the whole thing reads as geology instead of a person.
Rock is easy. A rock that can look worried is not. The plating has to break in a way that leaves room for an eyebrow to exist.
The heaviest passes, and a couple of the ugly ones, because the ugly ones are where the surface language got worked out.