eelings of disgust are often immune to rationality. And with good reason: evolutionarily, disgust is an incredibly adaptive, life-saving reaction. We find certain things instinctively gross because they really can harm us. Human secretions pass on disease. Noxious odors signal that your surroundings may be unsafe. If something feels slimy and sludgy, it’s likely a moisture-rich environment where pathogens may proliferate. Disgust is powerful, in short, because it often signals something important. It’s easy, though, to be disgusted by things that aren’t actually dangerous. In a prior study, Rozin found that people were unwilling to drink a favorite beverage into which a “fully sterilized” cockroach had been dipped. Intellectually, they knew that the drink was safe, but they couldn’t get over the hump of disgust. In another experiment, students wouldn’t eat chocolate that had been molded to look like poop: they knew that it was safe—tasty, even—but its appearance was too much to handle. Their response makes no logical sense. When it comes to recycled water, for instance, Rozin points out that, on some level, all water comes from sewage: “Rain is water that used to be in someone’s toilet, and nobody seems to mind.” The problem, he says, has to do with making the hidden visible. “If it’s obvious—take shit water, put it through a filter—then people are upset.”
