Ducks have an oil in their feathers which means that water is not absorbed by their feathers, but runs off them. This makes it easy for them to keep dry (spending most of your life in the water would be pretty cold and miserable if you were wet all the time). It also aids buoyancy.

My Grandfather used to work for Shell, the petrochemical company. He told me that Shell made a promotional film for a detergent they were working on. This detergent was shit hot at disolving oils in water apparently. So, in the film, someone sprays a little of this detergent onto a duck floating on a couple of feet of water. Apparently the duck sank pretty quickly. The oil in its feathers was gone and its buoyancy was reduced. I imagine that such a film would be banned today, which is a shame because it sounds hllarious.

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