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I'm not a zombie fan (other than the 60s rock group), so I haven't followed zombie movies too closely, but there's one question I have that I have yet to see answered here and answers seem to vary. And this isn't just about zombies starving.

I know there are different kinds of zombies, but still, they're all dead.

So what happens to a zombie that doesn't find humans with brains they can eat? It's not like the zombie will die. And, on a bigger scale, this brings up the question about what'll happen in other situations, like if a zombie were in a vacuum tank that was slowly depressurized so it didn't blow up, but would still find its skin and eyes and lungs boiling off.

Other than being dismembered or blown up, is there some way zombies just stop functioning? And if they stop functioning, say, by starving, can they be force fed or somehow returned to normal "zombie-ness?"

closed as too broad by Andres F., Jason Baker, alexwlchan, Rogue Jedi, Shevliaskovic Feb 23 '16 at 13:34

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    "Still, they're all dead" - much of the original idea of 'zombies' as they exist traces back to vodou, in which there are instances of both living and undead 'zombies' in folklore/fiction/history/etc. – Ian Pugsley Jan 31 '12 at 14:26
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    You want to force-feed a zombie until it returns to normal zombie-ness? That can't end well... – John C Mar 21 '12 at 11:38
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    +1 for the depressurized tank xD – Kalissar Jun 18 '13 at 8:10
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TL;DR (for my answer, not the question): Depends on the author.

There are multiple types of zombie. The majority are, like you say, dead.

28 Days Later and the sequel feature 'zombies' that are alive. These zombies are created by a virus called the 'Rage' virus, which drives infected people mad. They become hyper violent, incapable of higher reasoning, and are driven to cannibalism. They will starve if they don't eat, and likely die due to dietary deficiencies in short order (within years) even if they do. They can be killed through exsanguination, choking, or anything else that would kill a human.

The classic 'Romero' style zombie is seen in Night of the Living Dead and its various sequels. The books by Max Brooks (The Zombie Survival Guide and World War Z) codify them in great detail. These zombies do not need to eat. They are driven to devour flesh by instinct, not need. These zombies are perpetual motion machines - they will continue to function until they are destroyed, be it by a bullet or by decades of decay. Until they physically fall apart, they will continue to hunt to the best of their ability. Land of the Dead takes place decades after Night, but the zombies are still animate, still recognizable, and still a major threat.

The parody sequels, the Return of the Living Dead series, take it further: the zombies ONLY eat brains, and their teeth can open skulls like eggshells. They're reasonably intelligent, completely unkillable (excepting fire), and know how to order take-out.

Most other zombies tend to fall between the two extremes, though special mention should be made of the zombies in the Monster Island series - these zombies DO derive strength from what they consume. One that was locked in the elephant house of a zoo grew to massive proportions, and several that have recently eaten are seen to heal. They seem to be able to be restored to how they were at the moment of death, and if their blood is kept moving before they reanimate (to keep the brain oxygenated) they retain some measure of their intellect (and can manipulate the energies that animate them to use special talents). One zombie that was restrained, had their body mostly destroyed, and was left without food for years was able to revive fully after consuming the blood and flesh from a single goat (though this was explicitly said to be very unusual).

In short, zombies don't die unless killed...and killing them is hard.

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    Pet peeve of mine, the people in 28 Days Later and the sequel are not zombies. – NominSim Feb 17 '12 at 18:32
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    @NominSim: hence the quotes around 'zombies' when I discussed that movie. I agree, they weren't traditional zombies, but they fit the mold closely enough to be discussed. They're a relevant example for this question. – Jeff Feb 17 '12 at 19:27
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    @NominSim: They're relevant to the question at hand, zombies aren't always undead (see Ian's comment on the question). – Jeff Feb 17 '12 at 22:13
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    We'll have to agree to disagree, IMO a zombie by definition must be dead. – NominSim Feb 20 '12 at 14:59
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    I have to agree with Jeff. If you were asked for a list of Zombie movies, and you left out 28 Days Later, your list would be incomplete – GetSet Jul 16 '12 at 14:19
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Unless some kind of supernatural occurrence were involved, the zombies would pose much less of a challenge in real life as they pose in movies. However, movies would be very boring if everything were kept completely realistic.

A zombie caused by natural means (e.g. a virus, nothing supernatural) would perhaps be initially stronger and more resistant to damage than a human, but purely because we do not use our bodies to full effect. This is not without an important cause: we restrain our bodies' physical capabilities to avoid permanent damage to it. This means a zombie which does not feel pain would be stronger when still "fresh", but because of it, its "lifespan" as a functioning system would be greatly reduced. A human body is a complex and highly optimal system, when organs cease functioning / start rotting, the overall capabilities of that system will be greatly reduced. Without a functioning digestive system, (and without circulating blood to transport oxygen and nourishment) the muscles will not get enough energy.

There is no wonder why plants cannot move fast: they simply cannot produce the required energy (plants that throw seeds or close fly-traps build the tension for a long time). For such a strength and speed that human and animal muscles can provide, a constant supply of fuel and oxygen is needed, if the muscles don't have any fuel to "burn", they will not function.

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According to the World War Z novel, the zombie digestive tract doesn't work. Eventually they break down when their ligaments and muscle can't move anymore due to erosion by the elements or from their environment. Eating does not rejuvenate their bodies, and is a useless base instinct.

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    Not useless if it spreads the infection. – Beta Feb 17 '12 at 19:48
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    @Beta: True, but useless for the one who is already a zombie biting others. – Mufasa Feb 17 '12 at 23:25
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The "Brains" Trope:

As far as I know, the idea that zombies eat brains specifically and/or exclusively has its origins in the spoof/ripoff series Return of the Living Dead, which most zombie fans tend to either ignore or treat as the silly nonsense it is. Some zombie fanatics enjoy the series; others, like myself, despise it. In any case, the "official" zombie rules don't subscribe to the idea of brains being a zombie delicacy, although they would be as happy to eat fresh brains as any other kind of fresh meat.

Zombie Digestion:

To put it bluntly, zombie digestion doesn't exist. Zombies are, after all, dead. They are compelled to bite any animal that moves, including humans, and given the chance, they will "eat" flesh, but it doesn't actually benefit them in any way. This is a pretty consistent rule across the slow zombie spectrum; it is left unsaid in the classic 1968 Romero film Night of the Living Dead, but Romero gradually built upon the very vague and unspoken rules implied in NotLD, developing them into more concrete concepts in the sequels, like Dawn of the Dead, Day of the Dead, etc, until they were adopted by other writers, filmmakers, and enthusiasts.

However, it is important to note that the name "Romero Zombie Rules" is something of a misnomer, because Romero has never explicitly stated these rules, nor has he even condoned them; in fact, after the original NotLD, Romero has devoted his career to making zombie movies that break the rules bearing his name. As a zombie purist, I have no use for anything Romero has done since Dawn of the Dead, and even that is a poor follow up to Night of the Living Dead, which is almost universally recognized as the best zombie movie ever made.

As Romero slowly but steadily drifted away from the concept he had created, others stepped in to expand on the original idea and explain it in minute detail. The canonical "slow zombie" (also known as the Romero zombie) that we see today in franchises like The Walking Dead and the Max Brooks books World War Z and The Zombie Survival Guide were first envisioned by Romero, but they now owe more to Brooks than anyone else.

Why Do Zombies Do What They Do?

Max Brooks has provided us with the most comprehensive and convincing explanation of zombie physiology and behavior. His ideas have been borrowed by Robert Kirkman (creator of *The Walking Dead), Simon Pegg (Shaun of the Dead), and many others. The initial cause of the zombie pandemic varies from one source to the next, but in every other regard, the concepts are usually almost identical. For our purposes, we will have to ignore the unique twist introduced to the zombie genre by The Walking Dead - namely, the idea that everyone on the planet is already infected, and anyone who dies with their brains intact will become a zombie. We'll be focusing on the basic principle of bite = infection = death = reanimation as a zombie.

Brooks attributes the zombie condition to a virus called Solanum. He has described the virus in exquisite detail, but we can gloss over most of this and focus on the issue you have addressed in your question: biting, eating, and digestion.

To properly understand zombie behavior, you have to remember that zombies aren't people, or any other kind of animal. Zombies are vehicles for a pathogen (usually a virus). The rotting corpse shambling around and attacking people is basically like a car being driven by the virus. The person whose corpse has become a zombie is long gone, never to be seen again. The corpse has no thoughts, no feelings, no needs. It is just the virus' way of getting around and spreading itself to new host organisms.

The virus has to work with the tools at its disposal, which means that it reactivates part of the brain, but only the most primitive portions of the brain, and only the portions that will directly benefit it. The areas of the brain targeted by the virus are as follows:

  • The motor cortex: The virus needs a mobile host, so it makes sure that the zombie will be able to move around, grab things, and bite things.

  • The sensory cortex: The virus' only purpose is to infect other hosts, so it needs to make sure that the zombie can see, hear, and smell its prey.

  • The hypothalamus: The virus needs to make a dead body want to eat every living thing it sees, so it reactivates the hypothalamus, which is responsible for the sensation of hunger. Thus, the only feeling that might be present in a zombie is hunger, although this feeling does not correspond to conscious thought or problem solving as it would in a living person. The zombie doesn't actually think "I'm hungry, I should eat something"; it simply feels hunger.

These are all very primitive functions, and they don't require any conscious thought. But the virus still needs to make sure that its manipulations have the desired effect.

Remember, zombies aren't like us. If you get hungry, you eat until you aren't hungry anymore. The virus doesn't want its zombie host to get full and stop biting people, so it flips the hypothalamus' hunger switch to "On" and leaves it there. Zombies can't get full. No matter how much they eat, their hunger never dissipates.

In his book World War Z, Brooks describes zombies who have eaten so much flesh that their stomachs rupture, splitting the abdomen open and causing the already eaten flesh to spill out onto the floor. The zombie in question sees the meat that has just fallen out of his gut, and eats it again. It falls out again, and the zombie eats it again, until it has been dead for long enough for the zombie to lose interest. As if this wasn't gross enough, he also suggests that well fed zombies might eat so much flesh that it fills up the entire digestive tract and starts to force older meals out the "back door", so to speak. In most cases, however, the flesh a zombie consumes will simply sit in his stomach and slowly decompose.

The fact that zombies' hunger is never satiated creates a new problem: Since the zombie will never be satisfied with what it has eaten, it is inclined to keep eating until there is nothing left to eat. This doesn't help the virus' cause in any way - keep in mind that the virus isn't trying to feed zombies, it is trying to create new zombies. If a new host organism is found, bitten, infected, and then devoured entirely, the virus has just lost a chance to infect a new host. How does the virus handle this problem? By setting different priorities for the zombie.

The virus makes sure that zombies are fickle - they won't eat anything that has been dead for more than a few minutes. This minimizes the possibility of zombies wasting their efforts on bites that won't result in new infections. After all, the virus doesn't benefit from zombies biting things that are already dead; it only benefits if the bite victim is alive at the time it is bitten, and survives the bite long enough to turn into a zombie.

In a similar vein, if the zombie(s) see a living person while eating a previous victim, they will often abandon the kill and pursue the new target. This isn't always the case, but as a general rule, the longer the current meal has been dead, the greater the possibility that the zombie(s) will abandon it when presented with a new target.

This is a delicate balance between the zombies' compulsions and the virus' objectives, and since neither the zombie nor the virus are sentient, there is a lot of back and forth between the two. Still, it works well enough to accomplish the virus' objectives in most cases. As long as enough bite victims survive long enough to turn into zombies, the virus will achieve its goals.

So What Happens To Zombies Who Don't Eat?

Basically, the same thing that happens to zombies who do eat. They wander around as best they can until they either rot away completely or get killed somehow. We tend to think that zombies only die as a result of intentional attacks by humans, and although this is certainly what we see in zombie media, it isn't the whole story. Zombies can fall to their deaths, or burn to death, or be crushed by falling objects or even by each other (imagine a horde of zombies besieging a fortified position in which humans are holding out - the zombies at the front of the horde will be crushed against the walls by the weight of the horde behind them).

And although zombies are very resilient and resistant to damage, there are limits to their durability. According to Brooks, environment has everything to do with how long a zombie will remain active and dangerous. In a desert, the arid conditions will slow the process of decay, prolonging the zombie's "life"; In this environment, a zombie could remain active for a century or more. A frozen zombie will become harmless for an indefinite period of time, but if and when it finally thaws out, it will be just as deadly as ever, and none the worse for wear; it doesn't matter if the zombie was frozen for a day, a month, a year, or a millennium. In a tropical rainforest, the heat, humidity, and abundance of microorganisms will speed up the process of decay, and the zombie will rot away in a matter of a few years at most. In most cases, and under most circumstances, the average "lifespan" of a zombie is around ten years, give or take, and allowing for significant differences in the physical condition of the zombie and the environmental conditions in which it exists.

You might have noticed that, in discussing the longevity of zombies, I didn't mention the issue of whether or not they had access to food. There is a good reason for this omission: In short, it is totally irrelevant. A zombie that manages to eat an entire person every day for as long as it is around will not survive any longer than a zombie that doesn't eat anything for the same period of time. Because the zombie's digestive tract has been a puddle of rotten slime since shortly after it became a zombie, eating provides absolutely no benefit to the zombie.

How Can Zombies Die?

The most obvious cause of zombie death is the destruction of the brain, but there are other options.

  • If a zombie is exposed to extreme heat for a sufficient period of time, it will either die or be rendered harmless. If the cause of the zombie condition is a virus or bacteria, intense heat will destroy the pathogen. Even if the cause of the zombie condition is something that is not susceptible to heat, if you set the zombie on fire, the muscle tissue and nervous system will be destroyed, and the zombie will cease to be dangerous.

  • As mentioned above, crushing a zombie is usually enough to render it harmless, whether the crushing is deliberate or accidental.

  • Also mentioned above, zombies do decompose on their own, but it takes a very long time for this alone to permanently disable them. The only clear explanation for this, as far as I am aware, was provided by Max Brooks (of course). Brooks says that the Solanum virus has unique properties that discourage decomposition: Every form of animal life, including microscopic organisms, are instinctively repelled by the presence of Solanum. The same idea applies to most fungi as well. Therefore, whereas a normal human body will begin to decompose immediately after death, due to the runaway growth of bacteria, fungi, etc, associated with decomposition, the zombie is virtually immune to these organisms. By the same token, insects and other creepy crawlies don't try to eat tissue infected with Solanum. Animals will flee from the scent of it rather than trying to scavenge a meal. In short, the things that make human bodies rot so quickly don't like zombies, so zombies rot much more slowly. Still, zombies do rot, however slowly. So, as I said earlier, depending on the environment and other variables, the average zombie will be rendered harmless by natural effects after about 10 years, but the actual number can be significantly higher or slightly lower, again depending on the circumstances.

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Libris mortis, a D&D book, says that some types of undead require "food" to move. Zombies are not among them, but some movie zombies fit in this category of diet-dependent undead. Their need to eat is only a psychological, not a physical need.

Even if they go without "food" for an extended period of time, they won't die (again), and if they receive even a small amount of "food", they will start functioning normally again.

Regarding your vacuum tank and similar devices, they would kill a zombie if they damage its body beyond repair. You can freeze a zombie and then thaw it and it will "live" again, but if you smash it while it is frozen it won't be able to "live" again once thawed.

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