Darrell Ehrlich scanned the crowd of airport travelers for the look. The wide eyes. The slightly drooping jaw. The rubbernecking. That's when Ehrlich knew to make his move. "Can I help you?" (Lindbergh Field airport ambassador reads cues to help puzzled passengers find their way [Millican 1998:B-1].)
Facial expression. 1. A sudden and frequently sustained opening of the mouth visible in parted lips and dangling jaw, given in excitement, surprise or uncertainty. 2. An open-mouth position often seen in sleep. 3. A nonverbal sign to mock, challenge, or confront a foe. 4. A chronically open position of the mouth and jaw observed in the mentally challenged.
Usage: The jaw-droop is a reliable sign of surprise, puzzlement, or uncertainty. The expression is often seen in adults and children who a.have lost their way (e.g., in airports), or b. are entering or walking through unfamiliar, crowded, or potentially threatening places (e.g., darkened restaurants, taverns, and bars).
Observation. A sudden appearance of slightly parted lips signals mild surprise, uncertainty, or unvoiced disagreement.
Media. The jaw-droop is a staple of science-fiction thrillers, as a sign of disbelief or horror while confronting colossal apes, giant lizards, and alien spacecraft. Classic jaw-droop movies include King Kong (1933), Godzilla, King of the Monsters (1956), and Close Encounters of the Third Kind (1977).
Literature. "His lower jaw hung down as if lacking strength to assume its normal position." --Stephen Crane (The Red Badge of Courage)
Anatomy. In standard anatomical position (see BLANK FACE), the mouth is closed as muscle tone in masseter, temporalis, and medial pterygoid muscles is stimulated (in the awake state) by brain-stem impulses from the ascending reticular activating system to the trigeminal nerve (cranial V). In sleep, the chewing muscles relax and the jaw may droop of its own weight.
Muscles. Platysma, lateral pterygoid, and digastric muscles open our mouth as we gasp for air in shock or surprise.
RESEARCH REPORTS: 1. Darwin (1872) included opening of the mouth (along with pupil dilation, wide-eyes, and brow-raise) as a sign of attention and surprise, attributing it a. to muscle relaxation (as amazement "absorbs" bodily energy), and b. to drawing in a sudden breath of air (as the body mobilizes for protective exertion). 2. In "interest-excitement," the brows lift or lower slightly, the eyes open wide and fixate, and the lips may be parted (Izard 1971:242). 3. The lateral pterygoid muscles "are the prime openers of the mouth" (MacKinnon and Morris 1990:43).
Neuro-notes: Emotional stimuli related to surprise or horror travel downward from the limbic system through the brain stem to the trigeminal nerve to contract the lateral pterygoid muscles and open the mouth. Trigeminal is an emotionally responsive (i.e., "gut reactive") special visceral nerve.
See also FLASHBULB-EYES.