Lips which are slightly parted can be a strong flirting signal, particularly if the lips are then licked and even more so if done whilst holding the gaze of another person.
Parting lips is the first stage in speaking and may thus be a signal that the person wants to talk.
Lips which are pulled inwards from all directions are an indication of tension and may indicate frustration or disapproval.
Pursed lips are a classic sign of anger, including when it is suppressed. It is effectively holding the mouth shut to prevent the person saying what they feel like saying. This may also be an indication of lying or withholding the truth as the person stops themselves from telling the truth.
Pursed lips can also indicate a person who is thinking and who is deciding between possible options. Deciding and disapproval are both evaluative actions, which is the common core of lip-pursing.
A light puckering of the lips into a kiss shape typically indicates desire. It can also indicate uncertainty, particularly if the lips are touched with the fingers.
When you say 'oo', the lips form the kiss shape. This is one reason that romantic songs often linger on words like 'you' and 'too'.
When lips are sucked into the mouth or turned under so the red part of the lips are hidden ('swallowing the lips'), this can indicate that the person is thinking and uncertain about something, which could easily be bad news.
Lip swallowing can also indicate suppressed speech, where the person is preventing themself from speaking when perhaps they know they should. This can indicate lying or maybe disapproval.
Lips which are kept horizontal but squeezed flat are an exaggerated closing of the mouth (hence the name 'lip press') and may indicate a repressed desire to speak. This indicate disapproval ('If I spoke I would be very critical, which I do not want to be'). It can also indicate frustration ('I want to speak, but others are speaking and I feel I should wait').
Flattened lips can also indicate a refusal to eat, either because of dislike of offered food or some other motivation.
Another possibility is distress, where the person is trying not to cry or turn down their mouth in sadness.
When the corners of the mouth are turned upwards, this can be a grimace of disgust or a smile of pleasure. In a grimace, the teeth are unlikely to be shown (although toothless smiles are also common). Grimaces are often flatter and tenser.
A full smile engages the whole face, particularly including the eyes. Smiling with lips only is often falsehood, where the smiler wants to convey pleasure or approval but is actually feeling something else.
Corners of the mouth turned down indicates sadness or displeasure.
Some people are so miserable so often, this is the natural state of rest of their mouths (which is perhaps rather sad).
When the lips are pulled back, they expose the teeth. This may be in a broad smile or it may be a snarl of aggression. The eyes should tell you which is which. In a snarl, the eyes are either narrowed or staring. In a full smile, the corners of the eyes are creased.
Lips which are moving in the shape of words but without making sounds means that the person is thinking of saying the words. This subvocalization often happens with very small movement and is often completely subconscious. Stage mentalists use this when they ask their 'victims' to think hard of a word and then lip-read as they silently sound the word.
Up and down movement may indicate chewing. Some people chew the insides of their mouths when they are nervous.
Rolling in the lips so they roll across one another can be a preening gesture for women, evening out lipstick. It can also be a sign of uncertainty or disapproval (look for accompanying lowered eyebrows).
Small, lightning-fast movements of the mouth betray inner thoughts, for example a single twitch of the corner of the mouth that indicates cynicism or disbelief.
Liars in particular will often give themselves away with very brief grimaces as their conscience expresses disapproval of the conscious lies.
When the top lip is over the bottom lip, this may be linked with biting of the bottom lip, a common indicator that the person is feeling guilty about something.
The bottom lip extended over the top lip can indicate uncertainty, as if the person is saying 'umm'.
The bottom lip jutting out is often a part of a sulky pout, where the person expresses child-like petulance at not getting their own way.
Both lips pressed together and pushed out generally indicates doubt. If the finger touches them, it may indicate internal thinking or may say 'I am considering speaking but am not quite ready to talk yet'.
Biting the lip, centrally or at the side, is often a sign of anxiety. Usually, this is the bottom lip (especially if the person has overhanging top teeth). This may be a habitual action and people who do this, will often repeat the move in predictable situations. It can also be an indicator for stress during lying.
This is a fairly child-like action, especially if accompanied by wide eyes and eyebrows raised in the middle and lowered at the sides, and thus may betray concern about being told off or otherwise being censured in the manner of a child.
As well as a comforting action, biting the lip can be a suppressing action as a person is stopping themself from saying something.
Finally, the lips will have a position of rest when they are not pulled in any direction. This usually indicates that the person is also feeling relaxed.
