There are in English several situations where the words for animals differ from the words for their meat: Cow vs. beef, calf vs. veal, and so on. I've heard, repeatedly, that this came from the Normal Conquest: The Anglo-Saxon serfs raised the animals, calling them by more Germanic words; but their Norman French lords ate the meat, and used the French words for what they ate. People seem to like to trot out this explanation to display their erudition.
Well, it turns out that it's wrong.
Stephen Pinker, in The Stuff of Thought, says that this theory originated in Sir Walter Scott's Ivanhoe, when Wamba the jester, explained it to a swineherd ("Mynheer Calf... becomes Monsieur le Veau..."). Pinker references Burchfield's The English Language as stating that "Anglo-Saxon and French words didn't sort themselves out until centuries later."
I don't have a copy of Burchfield's book to check this (I'll be fixing that), but frankly I don't understand what Pinker's "sorting" statement means or how it relates to the issue.
A quick google, however, came up with a discussion on AskMetaFilter where others pointed out that many languages refer to animals with different words than those used for food, for example: Japanese ushi (cow) vs. gyuuniku (meat from a cow); Spanish gallina (chicken) vs. pollo (chicken meat).
Since there was nothing analogous to a Normal Conquest for those other languages, I think the French-origin legend is toast without getting Burchfield involved. But this does raise a question: Why is there a general, cross-language tendency to use a different word for an animal than for its meat? One possible very direct answer: Because they're different things. Duh.