Facial expression. A usually negative cue produced by pressing the lips together into a thin line.
Usage: Lip-compression is a specific version of the TENSE-MOUTH display. A sudden lip-compression may signal the onset of anger, disliking, grief, sadness, or uncertainty.
Observation. Barely noticeable lip-clenching may signal unvoiced opposition or disagreement. Like other lip cues, in-rolling is controlled by "gut reactive" special visceral nerves.
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RESEARCH REPORTS: 1. In rage, "The mouth is generally closed with firmness . . ." (Darwin 1872:236). 2. Apes express anger by staring, clenching the jaws, and compressing the lips (Chevalier-Skolnikoff 1973:80). 3.
In chimpanzees, a compressed-lips face "typically accompanies aggression" (Goodall 1986:123). 4. "In an aggressive mood, the
lips are compressed in a tense face with frowning eyebrows and piercing eyes" (Waal and Lanting 1997:33). 5. In the Highlands of Papua New Guinea, when men were asked to show what they would do when angry and were about to attack, "They pressed their lips together" (Ekman 1998:238).
source: http://members.aol.com/doder1/compress.htm (Sorry, I had to highlight the chimpanzee observation.
Here's another from the same site:
Facial expression. 1. A gesture produced by compressing, in-rolling, and narrowing the lips to a thin line. 2. A position of the mouth in which the lips are visibly tightened and pressed together through contraction of lip and jaw muscles.
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Observations. 1. Subliminal (i.e., barely noticeable) tension in a wife's lips prompts her husband to ask, "What's wrong?" 2. A CEO's tense-mouth face greets staff as they enter the conference room, creating a guarded atmosphere in which nobody speaks. 3. "Nothing's the matter," a boyfriend says. But his mouth's unusually thin line belies the point. His girlfriend asks, "Is there something we should talk about?"
U.S. politics. 1. The lips of a chronically angry, anxious, or intense individual may "freeze" in a permanently tight-lipped expression, as shown, e.g., in 1960s photos of FBI director, J. Edgar Hoover. 2. The tense-mouth is visible in AP photos of President William Jefferson Clinton, sitting in the Map Room of the White House on August 17, 1998, minutes before making a televised statement to the American people: "Indeed, I did have a relationship with Ms. Lewinsky that was not appropriate."
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RESEARCH REPORTS: 1. In Old World monkeys and apes, tense-mouth expressions convey threat and dominance (Van Hooff 1967). 2. Rolling the lips in is a socially avoidant cue in children (McGrew 1972). 3. In children, smiles in threatening situations are combined with tightening and compressing the lips (Stern and Bender 1974). 4. Monkeys and apes perform the tense-mouth with lips closed or nearly closed, mouth narrowed to a slit, and jaws tightly closed prior to an attack (Givens 1976). 5. In babies, lip-compression and brow-lowering (combined in the pucker face) appear when mothers persist in playing or feeding beyond an infant's tolerance (Givens 1978C). 6. Lip-compression (lips pressed tightly together and rolled inward) often appears in the company of strangers, where it correlates with gaze avoidance, non-contact, and distancing between individuals (Givens 1978D). 7. "You glance toward Mom at the other end of the table. You notice that her eyes are focused on Dad, and her lips are pressed tightly together. You brace yourself. You are about to get it. That look always means 'you're in hot water now!'"(Richmond et al. 1991:75). 8. The lip bite means "I am angry." The angry gesturer "bites his own lower lip with his teeth, shaking his head from side to side vigorously as he does so" (Morris 1994:154). 9. The tense-mouth is an aggressive sign in our nearest primate relative, the pygmy chimpanzee or bonobo (Waal 1997).
source: http://members.aol.com/nonverbal2/tensemou.htm
The homepage for this website is: http://members.aol.com/nonverbal2/diction1.htm#The%20NONVERBAL%20DICTIONARY
The dictionary covering nonverbal cues from the Adam's-Apple-Jump to the Zygomatic Smile is located here: http://members.aol.com/nonverbal2/entries.htm#Entries