One reason that horses have never been used primarily for food, Bellows said, was economic: A young horse had more use as a worker or mode of transportation, and once the horse got too old to work its meat was not particularly desirable. (Glue is another story.) Horses are also not particularly efficient in converting grass and grain into meat, which diminishes their desirability as food.

But the taboo in the United States is also tied to the perception that horses fall into or near the category of pets with distinct personalities. It's a perception that was reinforced in popular culture with television shows like "Mr. Ed" and the novel and film adaptations of "Black Beauty."

"We have this whole western thing where the horses were part of the whole western culture and the frontier," said Nestle. "And this whole romantic cowboy stuff. You don't eat your cowboy pets."

Compared to beef, there are not significant health risks to eating horse meat - indeed, there are those who hail it for being "low fat, full of protein" and delicious. Those who have eaten horse meat describe it as slightly redder, softer and sweeter than beef, though the differences are not glaring. In continental Europe, it is often made into sausages or cooked as a steak. (There are some concerns about the presence of a anti-inflammatory drug called phenylbutazone or "bute" in horse meat, though the risk from consumption is said to be very low.)

Horse meat is far from the only food taboo, of course - Many Islamic and Jewish people do not consume pork, for example, and most Americans would not eat cats and dogs - though humans appear to be the only animal that shies away from eating certain animals out of some sort of moral obligation.

James A. Serpell, director of the University of Pennsylvania's Center for the Interaction of Animals and Society, said "it's very difficult to think of a completely rational" argument for why certain animals are deemed acceptable to eat while others aren't.

"We have this tendency for a kind of morality that we apply to human beings to leach out to other species," he said, "and then the criteria for which it leaches out to is seemingly rather arbitrary."