One of McDonald’s most divisive products, the McRib, made its return last week. For three decades, the sandwich has come in and out of existence, popping up in certain regional markets for short promotions, then retreating underground to its porky lair—only to be revived once again for reasons never made entirely clear. Each time it rolls out nationwide, people must again consider this strange and elusive product, whose unique form sets it deep in the Uncanny Valley—and exactly why its existence is so fleeting.

The McRib was introduced in 1982—1981 according to some sources—and was created by McDonald’s former executive chef Rene Arend, the same man who invented the Chicken McNugget. Reconstituted, vaguely anatomically-shaped meat was something of a specialty for Arend, it seems. And though the sandwich is made of pork shoulder and/or reconstituted pork offal slurry, it is pressed into patties that only sort of resemble a seven-year-old’s rendering of what he had at Tony Roma’s with his granny last weekend.

These patties sit in warm tubs of barbecue sauce before an order comes up on those little screens that look nearly impossible to read, at which point it is placed on a six-inch sesame seed roll and topped with pickle chips and inexpertly chopped white onion. In addition to being the outfit's only long-running seasonal special and the only pork-centric non-breakfast item at maybe any American fast food chain, the McRib is also McDonald’s only oblong offering, which is curious, too—McDonald’s can make food into whatever shape it wants: squares, nuggets, flurries! Why bother creating the need for a new kind of bun?

The physical attributes of the sandwich only add to the visceral revulsion some have to the product—the same product that others will drive hundreds of miles to savor. But many people, myself included, believe that all these things—the actual presumably entirely organic matter that goes into making the McRib—are somewhat secondary to the McRib’s existence. This is where we enter the land of conjectures, conspiracy theories and dark, ribby murmurings. The McRib's unique aspects and impermanence, many of us believe, make it seem a likely candidate for being a sort of arbitrage strategy on McDonald's part. Calling a fast food sandwich an arbitrage strategy is perhaps a bit of a reach—but consider how massive the chain's market influence is, and it becomes a bit more reasonable.

Arbitrage is a risk-free way of making money by exploiting the difference between the price of a given good on two different markets—it’s the proverbial free lunch you were told doesn’t exist. In this equation, the undervalued good in question is hog meat, and McDonald’s exploits the value differential between pork’s cash price on the commodities market and in the Quick-Service Restaurant market. If you ignore the fact that this is, by definition, not arbitrage because the McRib is a value-added product, and that there is risk all over the place, this can lead to some interesting conclusions. (If you don’t want to do something so reckless, then stop here.)

The theory that the McRib’s elusiveness is a direct result of the vagaries of the cash price for hog meat in the States is simple: in this thinking, the product is only introduced when pork prices are low enough to ensure McDonald’s can turn a profit on the product. The theory is especially convincing given the McRib's status as the only non-breakfast fast food pork item: why wouldn't there be a pork sandwich in every chain, if it were profitable?

Fast food involves both hideously violent economies of scale and sad, sad end users who volunteer to be taken advantage of. What makes the McRib different from this everyday horror is that a) McDonald’s is huge to the point that it’s more useful to think of it as a company trading in commodities than it is to think of it as a chain of restaurants b) it is made of pork, which makes it a unique product in the QSR world and c) it is only available sometimes, but refuses to go away entirely.

If you can demonstrate that McDonald’s only introduces the sandwich when pork prices are lower than usual, then you’re but a couple logical steps from concluding that McDonald’s is essentially exploiting a market imbalance between what normal food producers are willing to pay for hog meat at certain times of the year, and what Americans are willing to pay for it once it is processed, molded into illogically anatomical shapes, and slathered in HFCS-rich BBQ sauce.

The McRib was, at least in part, born out of the brute force that McDonald’s is capable of exerting on commodities markets. According to this history of the sandwich, Chef Arend created the McRib because McDonald’s simply could not find enough chickens to turn into the McNuggets for which their franchises were clamoring. Chef Arend invented something so popular that his employer could not even find the raw materials to produce it, because it was so popular. “There wasn’t a system to supply enough chicken,” he told Maxim. Well, Chef Arend had recently been to the Carolinas, and was so inspired by the pulled pork barbecue in the Low Country that he decided to create a pork sandwich for McDonald’s to placate the frustrated franchisees.

But the McRib might not have existed were it not for McDonald’s stunning efficiency at turning animals into products you want to buy.

As McDonald's grows, its demand for commodities also grows ever more voracious. Last year, Time profiled McDonald’s current head chef, Daniel Coudreaut (I know what you’re thinking: two Frenchmen have been Executive Chef at McDonald’s? But no, Chef Coudreaut is American, while Chef Arend is a Luxembourger), whose crowning achievement so far has been turning a Big Mac into a burrito. In his test kitchen, we learn, a sign hangs that reads “It’s Not Real Until It’s Real in the Restaurants,” reminding chefs and cooks that their creations, no matter how tasty and portable they may be, must be scalable—above all else.

When the Time reporter visited the kitchen, Chef Coudreaut was cooking a dish that involved celery root—a fresh-tasting root that chefs love for making purees in the fall and winter. Chef Coudreaut proves to be quite a talented cook, but Time notes that “there is literally not enough celery root grown in the world for it to survive on the menu at McDonald’s—although the company could change that since its menu decisions quickly become global agricultural concerns.”

(Want to make enemies quickly? Tell this to the woman at the farmer’s market admiring the rainbow chard. Then remind her to blanch the stems a few minutes longer than the leaves—they’re quite tough!)