Via Boing Boing, a fascinating look at the elusive McDonald’s McRib sandwich:

The McRib is no longer needed as an emergency substitute for chicken. McDonald’s chicken supplies are now ample and stable, but the McRib still plays a role in bringing in patrons and their families that will come for the sandwich and nothing else. The amount of time it remains on the market is likely dependent on how much pork can be purchased at a profitable price.

Originally positioned as a way to entice diners who wanted Chicken McNuggets during early days when the supply was constrained, McDonald’s introduced the McRib. It didn’t do well in the United States, but continues to sell well in other countries. Today, it brings in diners who otherwise wouldn’t come to the Golden Arches, but follows a random interval schedule to enhance reinforcement coinciding with dips in pork prices.

Why Is the Mcrib Only Offered Occasionally and Why so Randomly?