When the gods looked down and spied lusty Ares entangled with lovely Aphrodite in the net which her grimy husband used to entrap them, there arose on Mount Olympus “unquenchable laughter”—in Homer’s words “asbestos gelos”. In the modern world, however, asbestos is no laughing matter: inhale the fibres of that mineral wool and you may contract asbestosis, a debilitating lung disease, or, as was discovered 30 years later, mesothelioma, a fatal cancer. Asbestosis is cumulative—you get worse the more you inhale—so that everyone who culpably fails to protect you contributes to your ultimate condition. Mesothelioma is quite different, for it is most likely caused by a single fibre: of course the more you inhale, the greater the risk of getting that fatal fibre, but until you get it, exposure makes you no more likely to get it, and once you have got it, you are a dead man, and further exposure makes no difference. Thus if you get mesothelioma after being exposed to fibres in six successive employments, each employer has contributed to the risk of your getting the disease, but the disease itself is due to only one of them. To ascertain in which employment the fatal fibre struck is, however, quite impossible and will likely remain so whatever advances are made in medical science, since the symptoms take up to forty years to manifest themselves, and before then no one can tell whether, much less when, the victim has been hit.