McDonald's Chicken McNuggets don't resemble any part of an actual chicken. This isn't an accident—the "random" shape of any nugget is actually one of four deliberate designs, and each one has a name.

According to Business Insider, Chicken McNuggets come in four shapes: the bell, the ball, the boot, and the bow tie (also called the bone). When the chicken meat that makes each McNugget is processed, it goes through a rolling cookie-cutter machine that stamps out the shapes. So the first nugget you take out of the box may look unique, but after eating enough of them, it won't take you long to find its exact twin.

Forming all McNuggets into the same four shapes serves a few purposes. By making them uniform, the fast-food chain can ensure the nugget cooks evenly within the standard cooking time. And because the shapes offer some variety, they appeal to kids. In addition to looking more "natural" than a rigid square would, the asymmetrical, curving designs are optimal for dipping.

That still leaves the question of why McDonald's settled on the number four when engineering its McNuggets. The company provided an answer on its website, writing, "The 4 shapes we make Chicken McNuggets in was the perfect equilibrium of dipability and fun. 3 would've been too few. 5 would've been, like, wacky."

The four McNugget shapes haven't changed in decades, but the ingredients inside them have changed many times. McDonald's even tested vegan McNuggets in Norway last year.

[h/t Business Insider]