Mouth - body language
The mouth is associated with very many body language signals, which is not surprising given its functions - obviously speech, but also those connected with infant feeding, which connects psychologically through later life with feelings of security, love and sex.
The mouth can be touched or obscured by a person's own hands or fingers, and is a tremendously flexible and expressive part of the body too, performing a central role in facial expressions.
Smiling is a big part of facial body language. As a general rule real smiles are symmetrical and produce creases around the eyes and mouth, whereas fake smiles, for whatever reason, tend to be mouth-only gestures.
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pasted smile:
A pasted smile is one which appears quickly, is fixed for longer than a natural smile, and seems not to extend to the eyes. This typically indicates suppressed displeasure or forced agreement of some sort.
tight-lipped smile:
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Stretched across face in a straight line, teeth concealed. The smiler has a secret they are not going to share, possibly due to dislike or distrust. Can also be a rejection signal.
chewing pen or pencil:
Like smoking and infant thumbsucking. The pen is the teat. Remember that next time you chew the end of your pen...
nail biting:
Nail-biting is an inwardly-redirected aggression borne of fear, or some other suppression of behaviour. Later nail-biting becomes reinforced as a comforting habit, again typically prompted by frustration or fear. Stress in this context is an outcome. Stress doesn't cause nail-biting; nail-biting is the outward demonstration of stress. The cause of the stress can be various things (stressors). See the stress article for more detail about stress.
biting lip:
One of many signals suggesting tension or stress, which can be due to high concentration, but more likely to be anxiousness.
