laugh and the world laughs with you,
Weep and you weep alone. . . . --Ella Wheeler Wilcox, Solitude (1883)

We never read of His laughing, though I am sure he did. --Billy Graham (1955:v)

Your mouth was twisted open, your tongue was stuck out halfway, your lips were pulled back and your nostrils were flared. Though you felt pleasure, your face suggested pain. Your cheeks turned red and you doubled over, gasping. Your stomach, chest and ribs ached. You were helpless, unable even to speak. --Robert Brody, "Anatomy of a Laugh" (1983:43)

Rhythmic vocalization. 1. Human laughter varies greatly in form, duration, and loudness (see, e.g., Ruch 1993, Ruch and Ekman 2001). A common form of laughter includes sudden, decrescendo (i.e., strong onset to soft ending), forced-expiration bursts of breathy vowel sounds (e.g., "hee-hee," "heh-heh," "ha-ha," or "ho-ho-ho") given in response to embarrassment, excitement, or humor. 2. In extreme form, an involuntary spasm of the respiratory muscles, accompanied by an open-mouth smile, flared nostrils, tearing eyes, facial flushing, and forward bowing motions of the head and torso. 3. In mean-spirited form, laughter (esp. group laughter) may be directed at enemies and persons with whom we disagree or dislike, as a form of aggression-out. This mocking-aggressive laughter resembles the group-mobbing vocalizations of higher primates.

Usage: To laugh is human ("Man is the only animal who laughs," noted the French philosopher Henri Bergson; but see below, Animal laughter, Primatology I). Chemically, according to some researchers, laughter provides relief from stress by releasing pain-killing, euphoria-producing endorphins, enkephalins, dopamine, noradrenaline, and adrenaline. Socially, laughter binds us as friendly allies united against outsiders, and against forces beyond our control. Psychologically, the comic laugh (in response, e.g., to funny jokes, puns, and satire) is a recent development perhaps linked to the evolution of speech (see below, Speech).