Bruxism

Bruxism (Noun): the habit of unconsciously gritting or grinding the teeth especially in situations of stress or during sleep

I notice it immediately. A person who wishes to label everything with textbook definitions would call it "bruxism." The masseter muscle quaking at the back of the jaw; thoughts hard at work. It's not unattractive when I catch someone unknowingly doing it. I just wonder how pitted their teeth must be.