The Artist's Complete Guide to Facial Expression Quotes

“The corrugator is the most human of the expression muscles. Some might argue in favor of the zygomatic major, the smiling muscle, but it's too easy to smile with nothing behind it. No one tries to cry, to be afraid, or to scowl with concentration - all expressions in which the corrugator is the main protagonist. ...
The smile can be a mask; when we use the corrugator, it's often because the world has broken through.

The smile can be a mask;”
― Gary Faigin, The Artist's Complete Guide to Facial Expression