Another one is eye contact; I generally don't have a problem making eye contact during conversation, but if I start thinking about it, I become aware that I can only look at one eye at a time and, I get a similar feeling of anxiety and discomfort. I can't decide whether to focus on one eye, switch between them (and at what rate?), or stare past the person, "magic eye" style so they look like a triclops.
It can be both maddening and very useful. But more than anything it makes you realize how comfortable you are with those closest to you, because all that overlaid mapping and planning fades away into actual casual conversation.
Veering far off topic now though!