How Do Zombies Know Where You Are?

24 Jun

I watched the World War Z movie on Friday, and there were a couple of scenes which got be thinking about how zombies know where people are. I won’t discuss the scenes themselves in case you haven’t seen it yet (and I’d definitely recommend doing so), but I think this is an interesting question and it’s one I’ll explore in this post. As humans, we are primarily visual animals and, for most of us, our eyesight is the main sense we use to find out about the world around us. To a lesser extent, we also use sound while our remaining senses, smell, taste and touch, are usually only used once we’re already aware of what’s going on.

With zombies, things might be different, but this will depend on the type of zombies we’re talking about. If we’re talking about living humans infected with some sort of disease, sight and sound will still be the primarily senses by which they will detected uninfected humans. The more traditional risen-from-the-dead type zombies, however, will be differ. While in some cases, it appears that these dead zombies can still use their sight, as a rule they seem to be less visual creatures. In particular, in many cases the eyes are specifically portrayed as being clouded over (as an indicator of death), meaning that such zombies are probably limited to seeing changes in light intensity rather than any actual images. This means the best they can probably do visually is detect movement and orient towards it. In contrast, sound seems to be a much more important sense for dead zombies, and in almost all zombie scenarios, it’s unintended noises which alert zombies to the presence of humans. There’s the possibility that such zombies might also rely more on other senses such as smell to tell if humans are nearby but given the limitations of the human nose, this will, at best, be an imperfect mode of detection.

However, when it comes to zombies knowing where you are, there’s more to this than just whether zombies can tell you are there or not. In particular, there’s the question of how zombies tell the difference between normal humans and their fellow undead, since almost every scenario presented in films and books suggests that zombies don’t attack each other. Well, I think there’s two options here. The first is through something like smell. If we’re talking about infected type zombies, many diseases cause humans to give off specific odours, and indeed this is the basis for diagnosis in some cases, while if we’re talking about dead zombies, they may also smell different because of decomposition. This means zombies could tell who’s normal and who isn’t by their scent. This possibility is the basis of the scene from The Walking Dead where the characters cover themselves in rotting flesh from dispatched zombies to allow them to walk through the undead which surround them. However, this would only work across small distances and it seems even over longer distances, zombies can tell the difference between their brethren and normal humans, pursuing the former while ignoring the latter. This suggests zombies can also tell the differences through movements. In almost all cases, zombies, whether fast or slow, and humans move in very different ways and these differences may allow zombies to identify their prey from a great distance. This possibility is the basis of the scene in Shaun of the Dead, where the eponymous hero and his friends cover the last few yards to the Winchester through a mass of zombies by mimicking their movements.

Yet, this still leaves some apparent problems. For a start, zombies seem to be able to know where humans are from greater distances than they could possibly see, hear or smell them, and they seem to be drawn towards areas of human habitation from great distances and across landscapes where lines of sight are limited. How else could you explain the hordes of zombies which tend to descend on and surround the safe houses where humans are hiding? Well, I think the answer here is what I’ll call the ‘vulture’ effect. Vultures hunt by soaring on thermals and scanning the ground below them searching for dead or dying animals. Yet, they don’t devote all their attention to what is going on below; they also watch the other vultures in the skies around them. When one detects food and starts to dive towards the ground, those around them know what this means and do the same, and so do the ones around them and so on. This means hundreds of vultures spread over great distances can descend on a potential food supply within minutes. Zombies, I suspect, would operate in a very similar way and when they hear or see other zombies reacting as if they’ve detected humans, they will be drawn towards the same point. This means that once one zombie detects your presence, you are likely to find yourself inundated within a very short space of time as all the zombies within the local area follow each other towards your location. Interestingly, this concept is depicted in the World War Z book, where they drop soldiers into a location, have them form a square and keep shooting until all the zombies which are drawn to the location from all over the place by other zombies are dead.

So what does all this mean for your survival if you’re unlucky enough to find yourself caught up in a zombie apocalypse? Well, firstly, if even one zombie detects that you are there, the vulture effect is likely to come into play, and many other zombies are likely to be drawn to you very quickly. This means you will only have a very short space of time to escape before you’re surrounded on all sides by hordes of flesh-munchers intent on tearing you limb from limb. If you can’t get away fast enough, there’s an outside possibility that you might be able to disguise yourself in some way so that the zombies can’t tell you are a normal human. You could try mimicking their movements or covering up your scent, but without knowing exactly how they are telling human from zombie this will always be a very risky strategy. In addition, this will probably only work for dead-type zombies and it’s unlikely that the infected type will be fooled so easily. In this way, infected-type zombies are probably more difficult to evade than the dead ones. Either way, however, your best chance of survival is to make sure the zombies don’t find out you’re there in the first place, so keep quiet and keep still!

From the author of For Those In Peril On The Sea, a tale of post-apocalyptic survival in a world where zombie-like infected rule the land and all the last few human survivors can do is stay on their boats and try to survive. Now available in print and as a Kindle ebook. Click here or visit to find out more. To download a preview of the first three chapters, click here.

To read the Foreword Clarion Review of For Those In Peril On The Sea (where it scored five stars out of five) click here.


5 Responses to “How Do Zombies Know Where You Are?”

  1. Serenity 24/06/2013 at 16:42 #

    I have always thought that zombies always knew where humans were by their smell, first and foremost. What smell? I am not sure. I don’t think it is fear or sweat, I think it is more primal, much more primal than that. I have always hypothesized that it was something like when an animals hunts another animal…or my favorite scenario I like to go back to is when raptors hunt out another dinosaur or easier for me to imagine is when those raptors hunted out those humans in Jurassic Park…by smell…but once again, what smell???
    As for the clouded eyes…you either see them clouded or dilated. It takes muscles to make your pupils constrict, so when you die, the muscles deconstrict and your eyes dilate. When light is shined into the eyes and the pupils dilate, it shows that there is brain activity. Zombies obviously have not brain activity. Eyes only cloud over just when conditions are right. Those conditions include temperature, bacteria colonizing in the eye, the eyes become soft and full of fluid, all which lead to the eye decomposing. This is the scientific explanation of the eye question. Hollywood just does whatever they want to do with the eyes that suits the scenario of the movie and how they want the shock effect of the movie.
    I was not trying to debunk your theories or derail your post, merely to comment on your post and offer my own hypothesis.
    Thank you for another awesome post!

    • cmdrysdale 24/06/2013 at 17:15 #

      You’ve obviously put a lot of thought into this, which is great. I had always thought that smell might be important until I started thinking about how good the basic human sense of smell is. Presumably, a zombie’s sense of smell can’t be any better that than of the human it once was. If this is the case, then no matter what scent humans give off, zombies wouldn’t be able to smell them from any great distance, and this is what would differentiate them from animals, such as predatory dinosaurs, which are specifically adapted to hunting by smell. Thus, my feeling is that a zombie velociraptor (now there’s a thought!) might be able to hunt by sense of smell but not a zombie human (at least not from any great distance).

      Your points about the eyes are interesting. I’d always presumed that eyes always clouded over to a greater or lesser extent, so it’s good to know the real situation (even if Hollywood does whatever it wants!). In terms of the irises relaxing (so making the eyes dark), this would presumably make their vision quite limited because the eye would have a wide aperture and so any light coming in would be unfocussed (I’m going by my knowledge of photography here). The muscles around the lens would also be relaxed, preventing it from doing anything to improve the focus. This would still suggest that visual detection is primarily related to detecting movement rather than by recognising objects. But then again, maybe I’m wrong here. What we really need to do is get a zombie and give it an eye test just to see how well it can see. Any volunteers?

  2. T.R. 24/06/2013 at 19:08 #

    Well thought out. Lots of things about Hollywood zombies make me raise my eyebrow. Lots of artistic license going on. I agree that clouded eyes depict lifelessness so its an obvious zombie marker. They do seem to be sight-feeders though. Since zombies must be cold-blooded any chance of them reading heat signatures? Do humans have that ability latent somewhere? And that begs another question. How do zombies avoid attacking each other? If you’re hungry you’re hungry. Many predatory animals have strong urinary proteins that identify them to other members of the hunting group, strong possibility that zombie pee is the ticket. If so that’s how you avoid being attacked. Spray zombie urine on you.

    Oddly enough I am finishing a zombie-like apocalypse book based on factual disease states that can cause something like this. I am looking for reviewers before I release it. It should be in final draft by the end of July. Would you like to get a copy to review?


    • cmdrysdale 24/06/2013 at 19:39 #

      These are some interesting points. I agree that zombies seem to be sight-feeders, but this is at odds with the apparently reduced vision. However, many real animals respond to movements (or simple changes in light and shade) and can key in on that even if they might be what we would call blind (i.e. they can’t really see an image as such, so maybe this is not necessarily a problem.

      I like the heat signature suggestion. I’m not too sure whether humans could ever detect heat with any existing organs, which would seem to rule this option out, but may be there could be some sort of change in the proteins in the light receptors in the eyes which would allow them to detect infra-red (heat) rather than just the usual red. This might be one at least vaguely viable option. If they could sense humans by heat signatures, this would also neatly solve the issue of why they don’t attack each other (since dead zombies wouldn’t have heat signatures – or at least they would have different ones to normal humans).

      The book you’re working on sound interesting. Email me at cmdrysdale [at] and we can discuss the possibility of me reviewing it further. It will depend on the exact timing of when you’d want it done by, and whether I can fit it in around various projects, as much as anything else.


  1. Hiding From Zombies In Plain Sight | Colin M. Drysdale - 26/03/2014

    […] it requires that zombies only recognise humans by sight and not by other senses such as smell (see this post for more information about how zombies know you’re there). This approach is probably only best used for short forays into areas where you might encounter […]

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