A Platypus Goes Blind on Purpose Every Time It Dives

A platypus shuts its eyes, its ears and its nostrils before every dive. Not because it sees badly down there. Because sight is in the way. Then it finds a shrimp the size of your thumbnail, in brown water, on a dark riverbed, in about thirty seconds. Then it does it again, around sixteen hundred times in one night. The bill is not a bill. A duck's bill is hard keratin. This one is soft, warm, leathery skin, carrying about forty thousand sensors that answer to electricity and about sixty thousand push rods that answer to touch and pressure. Every muscle in every living thing leaks a faint electric field when it moves. A platypus reacts to fifty millionths of a volt. Hold a nine volt battery in your hand and try to picture that. It buys her about eight inches of reach. Past eight inches, nothing. And here is the part that usually gets left out. The electric sense does not tell her where. It tells her that something moved. A shrimp that freezes is, to that sense, not in the river at all. If you like animals explained rather than animals dramatised, subscribe. One video a week, nobody shouting. 🔦 This video follows one female through a single night on a slow river in eastern Australia, and it asks one question: how does she measure distance in water she cannot see through? The answer, put forward by Pettigrew, Manger and Fine in nineteen ninety eight, is a stopwatch. The electric pulse from a moving shrimp reaches her almost instantly. The pressure wave from that same movement reaches her later. The gap between the two is the distance. Thunder after lightning, in the dark, forty times a minute. We also show where that model is still arguing with itself. Uwe Proske and Ehrin Gregory offered a different answer in two thousand three, and the measurement that would settle it has not been made yet. We say so out loud, twice. And we go back to seventeen ninety eight, when the first dried skins reached Britain and a Museum zoologist took a pair of scissors to the edg