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MANATEES have a sixth sense that works through a network of sensory body hairs unlike anything definitely identified in mammals before. Roger Reep of the University of Florida in Gainesville says that the hairs, which detect slight pressure changes, probably explain how manatees can navigate in dark waters and wait for incoming tides before swimming upstream. Reep and his colleagues report in a forthcoming issue of Brain, Behavior and Evolution that a manatee’s 3000 or so hair follicles are each connected to as many as 50 nerves. A typical human arm hair only has about five.