Those of us who do obedience work have known this for a while. Our dogs are more tuned in to our body language with verbal as a secondary/back-up. They are also tuned in to the tone we use with language, as much as the actual word.
Yes.. I think our smart Labradors have been "studying" us for years and they actually are professionals at predicting OUR patterns of behavior. Since dogs seem to see things in Pictures or sequences of visual cues I think they notice our breathing, eye gaze, body shifts, jaw tightening ...and more subtle things we don't even realize we do if what follows is rewarding to them or something they don't like.
Like all the little things you do before you take them outside, get their food , give them a bath, start dinner, start a play or training session, start loading the car for a show weekend.
Yes as an obedience trainer you learn this, I just think they are masterful at it.