Laughter.

My friend had a wedgie today, but instead of going about it discreetly she had to declare to everyone that her "knickers were getting a bit personal"

I laughed so much I cryed, but why? Is it really that funny? And if anybody else had heard her say that, would they have laughed as much as me?

Of course, me being me, this lead me to wonder about laughing. Why do people laugh?

Laughter is the biological reaction of humans to moments or occasions of humour: an outward expression of amusement.

Oh right, that settles it then, but what else?

Parts of the limbic system are involved in laughter. The limbic system is a primitive part of the brain that is involved in emotions and helps us with basic functions necessary for survival. Two structures in the limbic system are involved in producing laughter: the amygdala and the hippocampus.

Uh huh, and?

Laughter differs depending upon the gender of the laughing person: women tend to laugh in a more "sing-song" way, while men more often grunt or snort.

Sounds about right, anything else?

Laughter also gives your diaphragm and abdominal, respiratory, facial, leg and back muscles a workout. That's why you often feel exhausted after a long bout of laughter. You've just had an aerobic workout.

Ah I see, maybe that should be marketed as an alternative to the 'gym' I'd much rather laugh at a dvd of Peter Kay for ten minutes than sweat at the gym.