The platypus has confused naturalists since Europeans first encountered one in the late eighteenth century, a mammal that lays eggs, nurses its young, and carries a venomous spur on its hind leg. Wildlife filmmaker David Parer spent three years tracking the animal along Australia's east coast, filming in the rivers and creeks where it feeds and breeds. Underwater cameras catch it hunting, sifting mud for insect larvae and shrimp with the sensitive bill it uses instead of sight underwater, and record the mating ritual in which the male grips the female's tail and the pair spiral together through the water. The film's most difficult sequence comes from a nesting burrow: researchers fit a platypus with a radio transmitter to locate the tunnel, then drill careful access holes so infrared cameras can be threaded inside without disturbing the animal. What turns up is footage of behavior inside the burrow that had never been filmed before. The result is a plain, patient record of an animal that still does not fit neatly into any category naturalists have built for it.