Marty,
When I read someone its not in a situational context, its not like analyzing her every move, its basically looking at someone and getting a gut feeling as to who they are. Everyone has that ability as a child because its a protective attribute, and as you age that ability becomes dormant in most people.
Think about this: A man walks into the bank, heavy coat on, looks around spectating, has a rather "noticeable" look on his face, and you immediately know this guy poses a danger, and you pick up on that.
Well I do the same, but pick up on personalities, vibes, emotional states, and go from there. If a girl is walking past but intrigues my gut reaction, then I'm pulling her. If a girl is walking slowly but doesn't interest me, then I'm not doing shit with her
Does that clear things up?