BORED WHILE WAITING at the bus stop, Kate sticks a cigarette in her mouth just as she notices a billboard across the road. The small print reads, “Warning: Smoking causes lung cancer, heart disease, emphysema and may complicate pregnancy.” Kate stops for a moment. “How many have I had already today?” she asks herself. But then she lights up. “I don’t smoke that much,” she reasons, to quiet her conscience. “And anyway, I exercise and eat pretty well.”