Zombie lore is rich and varied. We’ve seen everything from the zombie as victim to the zombie as monster – from the slow, foot-dragging zombie to the World War Z-brand horrifying, super-fast zombie to the stupid, instinct-driven zombie to the problem-solving, tool-using zombie.

For the most part, the cardinal rule of taking out zombies is this: Shoot them in the head or strike a blow that results in a catastrophic brain injury. Prevailing wisdom is that the brain is the center of activity, even in the undead. Most zombie stories also center around zombification by way of virus. But let’s consider for a moment the real-life zombification that takes place in the natural world. Because it’s real.

It’s just not quite what you might imagine. IRL zombies aren’t typically infected by viruses, but are taken over by parasites who wrest control of their bodies, muscles, and nervous systems. Granted, we’re not exactly looking at cases of full-on zombie, but with the infection of certain parasites, observable changes in behavior, movement, motivation and cognitive activity have been shown: wasps taking over the bodies and minds of cockroaches, parasitic fungus changing the behavior of ants, a particularly nasty parasite called Toxoplasma gondii wreaking havoc on rats, cats, puppies, and people.

Parasites don’t necessarily creep in and infiltrate bodies in their entirety, but instead manipulate animal behaviors and personalities. It’s not arms-out, groaning, brain thirst, but it’s de facto zombie-ism.

What does that mean in the broader context of the zombie paradigm, though?

Well, it sure feels like there’s some untapped potential in zombies. Viruses are the popular route, but parasites present some intriguing possibilities. In fact, it’s parasites, even more than viruses, that really drive home the central theme and fear that resides at the heart of zombie stories: the loss of free will.

From the origin of the zombie, free will has been a key component, and parasites pose a direct and demonstrable threat to that free will. The original zombies from Haitian lore were reanimated by evil Bokor priests for slavery in the afterlife. But viruses don’t have a real motivator behind them. The virus doesn’t always have an easily understood motivation, beyond perpetuation. Parasites, at least, provide us with a living antagonist and a clear goal: survival.

Which brings us to the all important question: How do we kill them?

Well, the brain is probably still your best bet, considering that many of these zombifying parasites rely on manipulating brain chemistry. But you’re going to have to be thorough. IRL, taking out the brain is going to take out the host and you’d be good to go. Unless, of course, the parasite manages to survive and refocus its attack. But that’s another can of worms.

If we’re abiding by zombie theory, things may get a little complex. In zombies, we’re dealing with the undead — which means that while our zombies are moving and ostensibly “thinking” on some level, they’re not alive. This is where the undead stuff gets a little wacky. Brains need oxygen to perform, which means that our bodies need a means to get oxygen to the brain. While we’re alive, our blood does the job. But the oxygen starts with breathing – and zombies don’t breathe.

So, zombie brains function differently. We can make the assumption that in virus zombie lore, something in the virus changes the way the entire body operates (like a parasite!), and that includes the brain. Given what we know about zombies, it’s safe to say that zombie brains don’t need oxygen, and zombies still need brains.

When we replace the sort of parasite-like virus with a parasite proper, we come across some of the same problems. If we’re talking about the undead, we need to change the way that the brain operates on a fundamental level. Giving zombie lore the one-time exemption just like we do superheroes with powers that we can’t really explain, that means that we’re dealing with a different beast and that when were talking parasites, we might have to get a little more targeted.

A number of these parasitic zombifying creatures rely on specific parts of the brain and its chemistry. If we consider for a moment that zombie brains aren’t always an all-or-nothing affair (that is, sometimes you shoot them but you only get, say, part of the frontal lobe), you may find yourself with a walker that keeps on walking until you take out the basal ganglia — the part of the brain that controls movement.

Zombie lore is all hypothetical, but it’s worth considering how, exactly, one might contend with walkers that are animated not by a virus, but by a foreign species taking control of the body’s behaviors and functions. It also has us thinking about a fundamental shift in the way we look at zombies.

Parasites don’t often crawl into bodies and take over like that creepy little alien in the human body in Men In Black. Instead, they target an organism’s behaviors, subtly changing and manipulating certain parts of an animal’s personality. If, by definition, a zombie is an organism thats lost its free will and is moving, acting, and making decisions without said free will, then perhaps we could be among parasitically-created zombies right now and not even know it.

Photos via Paramount Pictures

Megan is a freelance writer whose work has appeared on WIRED, Slate, Travel + Leisure and GigaOm. When she’s not writing, she’s hiking, brewing beer, and extolling the virtues of The Cranberries.