It is an amazing thing to watch people laugh, the way it sort of takes them over. Sometimes, they really do struggle with it...So I wonder what it is and where it comes from, and I wonder what it expends out of your system, so that you have to do it till you're done, like crying in a way, I suppose, except that laughter is much more easily spent.
-John Ames, in Marilynne Robinson's Gilead