Girls giggle and guys grunt

Father Christmas has probably never gone "ho ho ho!" in his life. More likely, he just grunts, according to the largest ever study into the sound of laughter.

Jo-Anne Bachorowski of Vanderbilt University in Nashville, Tennessee, and her colleagues asked 97 volunteers to watch various film extracts, and secretly taped their laughter. Among the clips were the "bring out your dead" sketch from Monty Python, and the fake orgasm scene from When Harry Met Sally. "It's very fun, it really is," she says.

This left the researchers with more than a thousand bursts of laughter to analyse. "One of the biggest surprises was the variety of sounds that constitute laughter," she says.

Laughter can be "voiced" or song-like - such as giggles and chuckles - or unvoiced, like grunts and snorts. Most of the subjects produced a wide range of laughter types. But women produce voiced, song-like bursts of laughter more often than men, Bachorowski found, while men are more likely to grunt and snort.

Laughter clichés

The researchers also noted the vowel sounds in the laughter. These can be central - with the mouth more open - as in "turn" or "car", or non-central, as in "he" or "glow".

The team heard very few examples of non-central vowels, scuppering the idea that people often go "tee hee" or "ho ho ho". Other laughter clichés failed to hold up. "Stereotypes accounted for less than half of the laughter recorded," she says.

The subjects were all Americans, but Bachorowski says the findings may apply to other cultures. "I suspect that culture shapes the circumstances in which we use laughter rather than its features."