I often tap beats or rhythms with my fingers on an imaginary keyboard, like in my lap or something.... to a certain tune.... imagining the exact keys, sharps, flats, everything....
I bite the inside of my lip when I am nervous, sometimes till it bleeds....
A side effect of one of my medications makes the illusion that my skin is crawling, and so I feel itchy. I can usually ignore it, but when I get agitated over something, or lose my cool, I scratch my scalp vigorously and mess up my hair (I have a short, pixie cut which is a messy style anyway), to relieve the sensation.
When I concentrate hard on something, I purse my lips and shift them side to side, almost like a rabbit's nose twitching.
When I am reading, or focusing hard on some aspect of studying, from what I am told I get tis REALLY intense expression on my face. XD
These are my confessions....