What triggers laughter? What kind of joke induces hilarity? Very often, the accident does. As when a gesture or behaviour goes wrong, causing something unexpected to occur. When a moment strays and upsets the ordinary run of things. Certainly there are also thoughtful forms of humour, light and as if caressing, such as that of the very fine papier-mâché of the dress in Kiki Smith’s sculpture, Seated Girl with Owl. But let’s start with the most violent, the most radical: mad laughter, crazy laughter—full-throated, noisy, thunderous laughter. Laughter can be a form of excitement, an uncontrolled discharge of energy, a phenomenon linked to surprise. Laughter can seize you, more often in a very bodily, convulsive way. And everyone knows from ex...