Can Cass predict what your character is thinking/planning/doing? Snake exudes an air of calmness (and dry arrogance) almost constantly. I would say in general his motives and his body language will be more obscure than the average person's, but if he is caught off-guard and being emotional for some reason, it would be possible.

If yes, what limitations do you have on this? Due to his own observances of others being greatly defined by how a person walks, hold themselves and speaks, and his own naturally detached demeanor, Snake is more conscious of his movement, and thus more restrained - though he's also simply more naturally calm than he is really 'hiding' any impulses. His intentions are generally pretty straightforward - curiosity, mostly, though there can be layers to that. I just don't think he would be an immediate and obvious 'tell' in general.

That being said, to someone who picks up body language it will probably be fairly clear that Snake has a prosthetic left arm, though it is a very advanced.

Is there anything you'd rather she not be able to predict? His usage of telepathy and what he uses it for would probably be difficult to track, as it would come off as him 'looking' or 'listening' extra-hard, I think.

Anything else? You are a beautiful person. :)