In The Walking Dead (and most zombie movies), the zombies reanimate and then are able to walk again, eat again, and see again without respect to any injuries the person received before "dying." How does a reanimated being walk if the heart or certain muscles is destroyed? Clearly in many shots of the zombies we see little if any blood from the zombies. In the early part of the series, we would see half-stumps of people, dead people with large chest wounds, or dead people with partially eaten, injured or decomposed muscles that attempt to get Rick or other survivors.

What is evident is that circulation is not happening or possible in many cases. In living creatures, circulation of blood is what keeps motion possible. We know from having a foot or other limb "go to sleep" that we cannot move that limb until we get circulation back. Does the brain and nervous system become strong enough to "shock" the body into moving? how does that sustain without circulation? what happens then if the spine was severed?

Thanks for going on this trip with me!

  • 5
    It is a fictional depiction... They do not need to have circulating blood because that is what works.
    – Naftali
    Apr 3, 2013 at 13:57
  • 7
    No pathogen could animate them. The cells of the body/corpse require oxygen and other nutrients to survive, to be able to move. I favor supernatural explanations.
    – John O
    Apr 3, 2013 at 13:57
  • I feel like we discussed this, or something similar, but my searches are coming up empty.
    – phantom42
    Apr 3, 2013 at 14:05
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    AFAIK, The Walking Dead series / comics haven't tried explaining the biological particulars behind the zombies, but other mythoi have. Barring supernatural reasons, the Zombie Survival Guide comes to mind. They explained it by the zombie virus being a fungal infection that transformed the whole body into a mess of single-celled organisms that functioned both in tandem and separately. A bit sketchy on some of the details, it's still the most thorough sci-fi zombie explanation I've read yet.
    – jono
    Apr 3, 2013 at 14:21
  • 1
    Are you looking for an in-universe explanation? If so, then you should probably delete the "and most zombie movies" part. If, on the other hand, you are looking for a scientific explanation, then the answer is that the human body needs blood circulation to function.
    – Misha R
    Feb 10, 2016 at 4:44

7 Answers 7


One explanation (not specific to The Walking Dead) that I've seen offered is that not all circulation ends. Instead, it is only portions of the circulatory system that shut down (capillary and smaller veins and arteries).

Only the most essential main arterial paths remain in place, providing only enough circulation to handle a degraded level of gross motor function (providing a bit of a hand-wavy explanation for the stereotypical shambling gait and generally clumsy movements).

This also explains the atrophy of flesh, as the shut-down of the capillary system prevents sufficient flow of oxygen to skin tissue to keep it alive.

Perhaps a Walker with a destroyed heart would lose motor function, but this would likely take a bit of time for it to register with the limbs. I don't recall any direct and clear heart shots from the show, so I'm not sure if this theory is verifiable one way or another.

The Walker's movement still relies upon direct impulses from the brain, so severing the spine would stop all motion reliant upon connections below the point of separation. This is why direct brain trauma "kills" a walker, but decapitation leaves the head still "alive".

Of course, that also raises the question of how motor function is possible in a severed head, since clearly no circulatory system would be functional. The best hand-wavy answer I can come up with here is that the brain, being apparently the central source of the infection (if you remember from their time in the CDC center, we saw a recording of how the virus "activates" throughout the brain upon death), the virus can exert direct control over nervous system functions and also directly sustain tissue without need for oxygen delivery via blood steam.

  • 1
    I like this one as it explains the potential use of nervous system as a "shocker". I forgot how the CDC "explained" the infection workings. As far as show examples of destroyed or impaled hearts, I can think of a couple of them (Merle being one). Apr 3, 2013 at 15:32
  • @iowatiger08 Argh! I'm not caught up on the series!!! Don't tell me any more about Merle, please!
    – Beofett
    Apr 3, 2013 at 15:33
  • Apologies for My bad! Apr 3, 2013 at 16:28
  • No worries... its the hazard of falling so far behind in the first place.
    – Beofett
    Apr 3, 2013 at 16:29

The only "scientific" explanation I've ever been able to imagine would be if the virus/pathogen was somehow able to produce oxygen and other nutrients locally, thus sustaining some of the cellular functions of tissue immediately around it. Since decay of the body is still occurring, this ability to sustain cells is assumed to be limited, and you could even postulate that some cells (i.e. skin and fat) are allowed to decay so that the virus/pathogen could use those materials to sustain others (i.e. nervous and muscle).

  • I could go with this answer if the virus/pathogen were able to propagate around the body prior to circulation ending. Apr 3, 2013 at 14:40
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    @iowatiger08: That appears to be the case in the Walking Dead, since everyone's a carrier and it doesn't activate until they die.
    – gnovice
    Apr 3, 2013 at 14:51
  • Maybe the virus decays the cells and produces oxygen and nutrients locally as a byproduct?
    – CamelBlues
    Apr 3, 2013 at 19:21

There can be no muscle movement after death. Well, there can be muscle movement, if the muscles are stimulated with electrical current, but not the coordinated movement of movie zombies. Zombies are impossible, unless there is some supernatural force that animates them. Eating flesh cannot sustain them, as that implies metabolism, which is impossible if they are dead. The only explanation for the zombies we see in movies is either that they are not actually dead, but only subject to a pathogen that makes them insane and hungry for flesh, or that they are animated by some evil supernatural force.


If you go back to the episode in the CDC, Dr. Benner shows subject 19 and her (it was his wife) transformation into a zombie. According to Dr. Benner locomotion activities resurface. That may include circulation.


I realize this is an old thread but I ended up here so here's my theory: all biological viruses aside from perhaps the fungal one don't really work, the body needs blood for coordinated movement, and regeneration, although the zombies are usually decayed they would decay at a much faster rate than they do without blood flow. Aside from supernatural forces another explanation could be that the virus is actually machine based. All of humanity becomes infected by nanites that are essentially turned off/dormant. When someone dies the nanites' sensors detect no electrical impulses from the body and turn themselves on. They then control the body by hijacking the cns and relay electrical impulses throughout the body to themselves to control the muscles. This could also explains how a bite can turn an already infected person into a walker: when a living person with dormant nanites comes into contact with activated nanites, through saliva, (which is wear the nanites designed to spread infection could be stored) these nanites start turning on nanites around them and they start shutting down organs, the human immune system tries to fight this hence the fever, but ultimately dies. Upon death the reanimation process begins. This could also be why saliva from bites is contagious but no one gives a damn if they get walker blood in their mouth.

  • Aside from supernatural forces? This is a series about zombies after all.
    – Blackwood
    Dec 16, 2016 at 0:47

The cells of the body have both aerobic and anaerobic power sources. I have always pictured zombies as super anaerobic.

  • This reads more as a comment than an answer.
    – Jane S
    Feb 10, 2016 at 4:50

Zombies are a fungal colony that works by taking over the the structure of the body to seek out blood plasma (which is what the zombie fungal bacteria feeds on). Zombies or Zombie Fungal Colonies seek out living creatures to consume their flesh to get at the plasma from the blood. Because zombies have overtaken a dead body, the digestive system isn't working, so consumed flesh isn't digested, but instead, is either excreted out below through a compromised and rotting digestive tract, or vomited up to make room for more flesh. The act of eating flesh allows the colony to squeeze out the plasma from the bloody flesh before disposing of it to make room for more. The zombie bacteria isn't strong enough to kill people, but it does infect people and weaken their immune system so that they are more susceptible to disease or just weak to make them easier prey for the zombies. Once live flesh with the bacterial infection is consumed, those bacteria join the colony and give it strength, thus creating longer living zombies the longer they consume flesh.

  • 2
    That is true for the Zombie Survival Guide universe, but not necessarily for The Walking Dead.
    – FuzzyBoots
    Feb 2, 2015 at 20:41

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