A question out of idle curiosity and one which I have as yet to get a satisfactory answer, and I've asked it many times to many people. You might just be the one who is able to satisfy my curiosity.
Q/ If we are watching them for body language clues, what is there to suppose that 'they' are not watching us for the same cues? After all, as has been stated in some of the attachments to Leo's excellent posts, the accumulation of these clues is natural to any predator and cannot be disguised. If we are planning a pre-emprive strike we ourselves are just as predatory, if not more so than our opponent so the clues will be there for them to spot also.