ZOMBIES: THE HORROR ICON OF OUR AGE. The reanimated bodies of the freshly dead, shambling and shuffling with empty eyes and open mouths, searching for the flesh — and especially the brains — of the living. The sublime horror of seeing our friends, family, and loved ones return from the dead only to seek to devour us. The dread that if we, too, are infected, our fate will be the same as theirs: to roam the Earth in the rotting shells of our bodies, spreading death and terror before us.

Only one problem: it’s impossible. “How can that be?” you ask. “The movies/books/TV shows are full of scientific explanations for how these zombies have all appeared and are desperate to crunch through our skulls to the tasty filling! It’s a virus/radiation from space/mutated parasites/some other explanation.”

Thing is, movies/books/TV shows only have to give enough of an explanation to make you stop thinking it’s nonsense. So giving a plausible explanation is part of any fictional movie/book/TV show, whether it’s a soap opera or a zombie apocalypse. Whether it’s believing that the hot guy and hot gal who hated each other before the first commercial break will end up in bed before the final credits, or watching ravenous hordes of our decaying friends and neighbors knock down our doors and windows to rend our flesh with their teeth, we have to have just enough belief not to question every page or episode. Because that’s how fiction works— through the willing suspension of disbelief.

Herewith, then, are the reasons why a zombie apocalypse is, and will always be, fictional:


Dead bodies can’t burst from their graves. It’s a wonderfully eerie part of most zombie movies: The earth atop a grave begins to swell, then vibrate, then break apart, and out thrusts a grisly, decomposed hand, followed by another, and then the head and torso of the zombie breaks forth to eat the brains of the living.

Except they can’t actually do that. Even living people can’t break out of their coffins and claw through six feet of earth. Disagree? Tell that to a man known only as “Jenkins,” from Buncombe County, New York. His corpse was exhumed in February 1885; his body was found to be turned over onto his stomach; his hair was torn out, and scratch marks were found on the inside of his coffin. He had been buried alive, and his struggles to escape were futile. Or consider a woman (last name Collins) from Woodstock, Ontario, Canada, who in January 1886 was disinterred only to be found with her knees tucked up under her body and her burial shroud ripped into shreds. Their deaths must have been horrific: confined in a box with no light, covered by six feet of earth making it impossible to lift the lid, each breath using the last available air until their gasps eventually stifled them in a suffocating panic…


“But those were living people!” you no doubt respond. “Zombies could keep going because they would already be dead and wouldn’t need to breathe!” Which raises the next point.



Muscles need oxygen to function. In fact, here’s how muscles work: the living body sends glucose (sugar) to the muscles through the circulation of the blood; the glucose is turned into adenosine triphosphate (ATP), which gives the muscles energy. It’s called cellular respiration, and it’s the basic chemistry of how living things work.

But while there are some microorganisms that don’t use oxygen for cellular respiration, humans aren’t in that class. We require oxygen to create ATP, which is what causes muscles to contract. So let’s go back to that zombie who has just been reanimated in his coffin. Sure, he’s dead, so the whole “suffocating panic” thing doesn’t apply.

While a living human who wakes up in a coffin will eventually die from oxygen starvation (which first causes the brain to cease functioning, then the nerves, and finally the muscles— remembering that the heart is a muscle), an already-dead zombie will also eventually run out of oxygen to fuel cellular respiration. Result: no more muscular movement to push through the soil and breathe once more the sweet, sweet air of the living. So even if the zombie virus/space radiation/mutated parasite inhabits the central nervous system of the host and causes the nerves to fire (see point 4), the lack of oxygen in the muscles means there’d be no movement.

“Well, what about a dead body lying on the ground?” you ask. “Surely they would have access to oxygen!” True, they would … but there’s a fundamental issue with that, too.


Oxygen has to get to the muscles. The circulatory system (that is, the heart and blood vessels) take glucose and other nutrients to the muscles and take away carbon dioxide as the waste product. This means that the zombie would have to be breathing, taking in fresh air and exhaling carbon dioxide. But of course, that wouldn’t do either, because for that to work the heart also has to be beating, making the blood pump through the arteries and back through the veins. Which sounds an awful lot like not being dead. Since the whole point of being a zombie is that they are dead, and then they start wandering around chomping people and making more zombies, there’s a fundamental conflict: Zombies, being dead, are typically described as having no pulse. No pulse = no circulation. No circulation = tissue death. And that leads to…


Dead tissue can’t move. Cellular respiration requires living tissue, because the chemical reaction required to make a muscle move requires those muscle cells to be alive. Once tissue death (also called necrosis) occurs, it’s not reversible. That’s sort of the definition of death: yes, if the heart stops briefly we can sometimes restart it, with a defibrillator or CPR or other mechanical means, but once the cells start to die, those changes are permanent. You can’t turn chicken soup back into a chicken. So let that virus/space radiation/mutated parasite zap those nerves to its heart’s content (assuming it has a heart, but that’s another question entirely): eventually the tissue will be dead, at which point no amount of nervous stimulation will cause the muscles to move. And similarly, once the nervous tissue itself is dead, no amount of stimulation of the dead nerves by virus/space radiation/ mutated parasite activity will transmit signals down the neural pathways.

“But what about that guy who electrocuted the dead frog?” some of you are asking. You’re no doubt remembering Luigi Galvani (1737- 1798), famous for having touched a scalpel charged with static electricity to the sciatic nerve in the disembodied legs of a frog, causing them to twitch and jump. This, of course, led directly to Mary Shelley’s Frankenstein, which of course involves the reanimation of dead tissue, though, of course, her monster is more a patchwork quilt of body parts than a true zombie.

However, the key to Galvani’s discovery is that he was skinning a freshly killed frog when the electrified scalpel touched the exposed nerve. In my own misspent youth, I was able to keep the surgically excised heart of a freshly killed frog alive, in a solution of its own blood mixed with fresh water, for nearly 30 minutes before motion completely ceased. (Full disclosure: I did not perform experiments at the time to determine whether the heart stopped beating because of cell death or because the oxygen and glucose had been eliminated. Hey, I was eight years old at the time.) The key words in my own grisly experiment and in Galvani’s more famous one are, of course, “freshly killed.” Because once necrosis sets in, you’re on the way to the final destination…


Here’s where things get ugly (yes, even uglier than an eight-year-old kid watching a frog’s heart beat for half an hour in a glass jar). Scientists classify decomposition into five stages: fresh, bloat, active decay, advanced decay, and dry/remains. The fresh stage begins—you guessed it—the instant the heart stops beating. First, blood (no longer being pumped) pools in the lowest parts of the body; within three to six hours, rigor mortis sets in and the muscles stiffen; rigor mortis can last for 20 to 30 hours, depending largely on the temperature.


More importantly, without oxygen going in and carbon dioxide going out, the body becomes more acidic; cells lose their structural integrity and release enzymes that start breaking down the tissues. At this point, what was once muscle gradually becomes a kind of thick soup, and even the connective tissue holding bones together can soften. Finally, the “fresh” stage ends as bacteria in the body start to consume the body’s carbs, fats and protein, in a process called putrefaction, which leads to bloat.

Let’s just say things don’t get better from here, neither for the decedent nor for the zombie enthusiast, because the next stages (as fans of forensics shows know) involve calculating time of death based on what is least disgustingly referred to as “insect development,” among other things. (A perennial favorite: as fluids are purged from the body during active decay, they create what forensic scientists call a “cadaver decomposition island,” or CDI, in which natural vegetation is suppressed by the grisly liquids exuded by the decomposing cadaver.) But basically, once the heart stops beating, the process of decomposition begins immediately, and within an hour or so, various critters—microbes, insect larvae, or if you’ve had the bad fortune to perish inside your home, your chihuahua suddenly deprived of its accustomed cans of chicken parts in tuna—begin to consume your flesh.

Even if a virus/space radiation/mutated parasite were to take control of a freshly killed body, there would only be a very limited time period during which the body would be capable of even rudimentary movement. Galvani’s frog may have twitched or even kicked when touched with a scalpel, but it didn’t grab a top hat and cane and start dancing the Michigan Rag. And within an hour or two, the muscles of our not-quite-a-zombie would stiffen up, making it impossible for any shambling, shuffling or other horrifying antics. Lastly, within 30 hours at the outside, bits of our not-quite-a-zombie would begin falling off, either because putrefaction had softened the tissues or because “insect development” had consumed enough body mass that there simply wasn’t enough left for the not-quite-a-zombie to stand up, let alone bite through your skull for the delicious grey contents.

So fear not the zombie—at least, not until you walk past a graveyard at night and wonder what that flicker of activity just outside your field of vision really was. Surely just a leaf blowing in the nonexistent wind … a cat on the prowl … something far less terrifying than the pounding of your heart and the rushing of your breath makes you think it is. Pleasant dreams!


Editors Note: A version of this article first appeared in the January 2015 print issue of American Survival Guide.