Assumptions are your wonderful gift to the Earth :). Most of those assumptions do not particularly make logical sense, but good job you winner! Winners do not deal with stupid, boring truths, they just make shit up as they go along, right? YAY!
While the mouth may be saying one thing, the eyes may be saying another. Take fake smiling for example.
A person's eyes can usually give away if the smile is fake or not. The eyes can also determine other things that a facial expression may be trying to convey deceptively.