Foie gras is an old traditional delicacy from the French cuisine. Directly translated foie gras means “fatty liver” and is the liver of either a goose or a duck.
The picture shows a normal duck liver (right) versus a foie gras liver (left). It is obvious that there is a big difference on these to livers. The difference occurs in the way the birds are fed. To obtain the fatty liver the ducks and geese are force-fed. A tube is forced down their stomach through the gullet of the bird. Fortunately there are farmers who use a more organic and humane production method.
This video shows how foie gras is obtained by the force-feeding of ducks/geese. Warning against strong pictures.
The video is made by PETA, an American animal rights organization.