Facial grimacing is a simple motor tic
Grimacing, as an adj. would mean frowned, contorted, diapproving, wry.
the grimace on her face showed how angry she was.
tourette syndrome
A caninus muscle is a a facial muscle of the mouth
zygomaticus major muscle (a facial muscle)
Grimacing is a verb.
The Frontalis muscle .
The Buccinator muscles. (The cheeks)
The orbicularis oris is the facial muscle responsible for puckering or pursing the lips.
lanax
The platysma muscle is the only muscle located directly inside of the skin. It's function is to, along with many facial muscles, allow a person to mimic, or create facial expressions.