Epidemic. A man on my subway train starts to laugh. First a trickle, then a fountain, then a flood of good-natured and sincere laughter. The man's laughter has no observable object, no context. He is clearly mad. Passengers around him try on some dirty looks, seeming more confused than annoyed, but soon give up. Then a group of schoolkids starts to snigger at the laughing man and, presumably, at the effect he is having on their fellow passengers. The sight of children ridiculing the insane disquiets more onlookers; one woman lets out a few nervous titters. The man's ringing peals have now subsided for reasons as mysterious as their origins. And taking in the whole situation, I let out a little sigh of recognition. And again, the man begins to laugh.