body language is a big give away because most ppl dont even realize they are doing it... might sound weird but ive taken many classes about body language.
ive forgotten a good bit of since it was dam near 4 years ago but one thing that stood out was that the way a persons legs are pointed while in a relaxed sitting postion usually point to the person that they are thinkin about even tho they may not know that person is actaully on their mind