For almost uniquely, in the repertoire of modern Western cuisine, the oyster is eaten uncooked and unkilled. It is the nearest thing we have to "natural" food---the only dish which deserves to be called "au naturel" without irony. Of course, when you eat it in a restaurant, its shell has been barbed and unclamped with all the panoply of civilization by a trained professional, wielding appropriate technology, an inviolable ritual and a stylish flourish. Before that, the oyster was reared underwater on a stone tile or wooden trellis, herded in an oyster bed, grown for years under expert eyes and harvested by practical hands---not plucked from a rock pool as a prize seized from nature. Still, it is the food that unites us with all our ancestors---the dish you consume in which is recognizably the way people have encountered their nourishment since the first emergence of our species.--from Near A Thousand Tables: A History of Food.
More about oysters here.