Some time ago at work, I verified a system design by running the whole thing in my head, bombarding it with various fault conditions in all phases in order to check whether I had forgotten anything. I had my eyes closed, and my PC was not even switched on. Right in that moment, the boss of my department came in.
He: what are you doing?
Me, without opening the eyes: thinking.
He: don't you want to code?
Me, eyes still closed: no.
He: (leaving)