The decision on the EU Referendum (Brexit) will be made in the next few hours. David Cameron is, of course, the lead advocate of the "Remain" camp. Thus these expressions are very probably representative of the Prime Minister's emotional tone at this moment.
In the first image (above), Mr. Cameron is displaying an “Inward Lip Roll (ILR). An inward lip roll is just one of many nonverbal tells signaling that the emotion being felt (or though-felt) is significantly greater (and/or different) vs. what is being expressed verbally. Such verbal-nonverbal disparities are profoundly important glimpses into another person’s mind - as well as our own when we're projecting body language/facial expressions.
As its name suggests, during an ILR the lips are rolled inward and gently (to moderately) bitten. In all but the milder examples, this is also accompanied by a jaw jut (jaw pushed outward) along with a wrinkling/dimpling of the chin. The “mustache area” is also tensed as this mid-facial tissue is put on stretch. In addition, there usually is at least a mild-moderate degree of nostril flaring (as is seen in this example).
In the setting of an inward lip roll, the psyche is attempting to suppress strong feelings from building up as well as suppressing these emotions from being expressed outwardly. The ILR is usually associated with negative emotions such as anger, anxiety, sadness, etc., however it's also one method we all commonly use (most of the time subconsciously) in preventing laughter or smiling out of social context.
In this second image, Prime Minister Cameron’s facial nonverbals are similar, yet somewhat more developed. Note the additional finding of a more reddened facial color - including his ears. This betrays the presence of a valsalva-like phenomenon of semi breath-holding and increased intrathoracic pressure resulting in a temporary pooling of blood in the head/face. This also causes the distention of the jugular vein (seen in his left neck). If we had a blood pressure monitor hooked up to the PM, we would see a significant rise in this moment.
Intriguingly, those individuals who regularly practice yoga and other meditative activities will have this facial expression much less frequency.
Whenever observing nonverbal behavior, it's extremely important to never interpret in isolation and always look at the other components of a person's over-all body language. What do David Cameron's eyes say about his total expression? If his eyes were opened very widely with these same mouth configurations, what emotion would that indicate?
See also:
Nonverbal Communication Analysis No. 3596: Blake Lively, Ryan Reynolds and Deadpool
Nonverbal Communication Analysis No. 3591: Jo Cox, The Brexit and Sincere Smiles
Nonverbal Communication Analysis 3586: Barack Obama, Jimmy Fallon, Alpha-Beta Hybrids and Body Language
Nonverbal Communication Analysis No. 3577: Tape Face - America's Got Talent 2016 Auditions
Nonverbal Communication Analysis No. 3573: Angela Merkel, the G7, Destroying Rapport and Body Language
Nonverbal Communication Analysis No. 3531: Helen Mirren, Subways, Sincerity, Empathy and Body Language
Nonverbal Communication Analysis No. 3509: Bernie Sanders meets Birdie Sanders
Nonverbal Communication Analysis No. 3473: Adele's Tongue, Ellen DeGeneres and Body Language
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