Yeah, if you know a person well, and you treasure them, you notice those little things. I remember when I was little, there was a time when I was fairly angry during class and my best friend at the time asked, "Are you angry?" and I was like: "No..." It surprised me that he could tell, 'cause I thought I was hiding it pretty well.
So if you have a friend like that, treasure them. I did not... now I really miss those times and have no one to blame but me