Laughter.

"Laughter is the thing that clenches your stomach muscles and makes you wince like a leaf folding in two due to dehydration."

Right....not sure that it's a good thing then according to that statement. Lets try another.

"Laughing is what you do when someone falls over."

Yes...but I was looking for something a little more in depth than that.

"Your laugh comes from your guts, only when you find something truly funny."

Ummm...anyone else thinking quotes can often be crap.