In Blade Runner (1982), Deckard used the Voight-Kampff test to detect Replicants. This complicated test verified if their emotional response was appropriate. But they also displayed superhuman capabilities, were shown to take a lot more damage than humans can, and so on.

Why is it so hard to detect them if they have enhanced physical capacity? Wouldn't that enhanced capacity imply some physiological difference? Or why not just test their capacity directly?

  • 7
    Personally as a human, I wouldn't want my "physical capacity" to be tested on a replicant scale just because someone's paranoid I'm an android.
    – Tacroy
    Oct 19, 2012 at 16:16
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    @Tacroy How could I be sure you are an human? Jump on this VO2 max right now and run!
    – DavRob60
    Oct 19, 2012 at 16:18

5 Answers 5


In the book, Do Androids Dream of Electric Sheep?, it is said that androids can be detected with a bone marrow sample.

However, the police cannot by law do it on someone on mere suspicions. The Voight-Kampff test is non-invasive, so it's a far preferable method.

  • I had forgotten that; good catch! It seems like its time for me to re-reread that book again...
    – Beofett
    Oct 19, 2012 at 16:48
  • I find it hard to believe that in world with the capacity of making such advanced machines, they don't even have TSA-style scanners to distinguish humans from androids.
    – Pier
    Oct 7, 2013 at 17:52
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    another test used is based on the speed of the electrical message going from the hand to the brain. But The Novel say that the only definitive test is bone marrow sample
    – Edelk
    May 9, 2017 at 15:06
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    @Pier: The word "android" in the novel is used in a different way than what we consider androids today (thanks Star Trek!). In the book androids are merely humans that have been engineered at the cellular level. Note: they're 100% human except that they were never born from a human womb. Androids are machines in exactly the same way you are a machine.
    – slebetman
    Oct 12, 2017 at 9:54
  • Thanks @slebetman I read the book a long time ago but I don't remember that. Hm I should reread it.
    – Pier
    Oct 12, 2017 at 15:34

It is much easier to fake a lower capacity than a higher capacity.

How do you test for superhuman strength? All a replicant would have to do is say "this is too heavy for me!" even if it wasn't. You can't put them in situations where they would be harmed by not demonstrating superhuman strength, because anyone who wasn't a replicant would therefore be harmed.

How do you test for an increased capacity to sustain damage? You can't go around beating or shooting people and measure how well they survive.

Even a detailed physical examination is unlikely to detect physiological differences. As we saw from the scene with Chew, the body parts are organic, and the result of genetic engineering. You can't do something as simple as run them under a metal detector.

The most reliable way is to focus on what replicants can't do as well as humans, and that is demonstrate a normal range of emotions.

  • 1
    Interesting side note: "All a replicant would have to do is say "this is too heavy for me!" even if it wasn't." is actually hard to do repeatedly without some kind of feedback concerning how much [weight|range of motion|...] is actually involved. Insurance fraud types sometimes subject people with claims of "back pain" and other non-obvious injuries to blind tests in hopes of detecting false claims. But maybe replicants are better at it than natural humans. Oct 19, 2012 at 17:29
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    I was thinking about the Salem Witch Trials as similar tests... If they died during the test, it would be proof enough they weren't a witch... At least they'd get buried in consecrated ground... Oct 20, 2012 at 0:31

I do not think that anything depicted could be considered "superhuman". While the average overweight Cheetos-eating couch potato would be incapable of these feats, they're all within the limits of what's humanly possible (though at the edge). Extraordinary athletes in peak condition would be able to match them.

In other words, the structures and muscles that allow them to do this won't appear inhuman when examined. Probably not even under a microscope.

Hunting for replicatants in this fashion would be identical to getting rid of every exceptional athlete in the world.

  • Are exceptional athlete able to grabs a boiling egg with her bare hand without harm?
    – DavRob60
    Oct 19, 2012 at 16:33
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    @DavRob60 Read the last sentence of the section you linked. If you consider "insane" to be a subset of "exceptional", then perhaps the answer is implied to be "yes".
    – Beofett
    Oct 19, 2012 at 16:43
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    I don't think there's such a thing as "Blade Runner canon", but if there was, I doubt that would count (mostly because I haven't read it :P Regarding the egg scene, keep in mind that it can take hours, or even days, for the damage from a burn from boiling water to show. Of course, we see her later, and I don't recall seeing her bandaged... so: possible, yes. Plausible, no.
    – Beofett
    Oct 19, 2012 at 16:59
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    @Beofett: I suspect that many psychopaths would fail the Voight-Kampff test as well.
    – ruakh
    Oct 19, 2012 at 19:30
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    @ruakh You're probably right.
    – John O
    Oct 19, 2012 at 20:26

I know this is an old thread, but I don't think we've explored one possible physical difference - resistance to high and low temperatures.

In one scene, Leon puts his hand into a deadly freezing substance, but doesn't suffer any effects. In another, Roy puts his hand into boiling water. Wouldn't their skin have to be different to withstand that?

If it was, you should be able to take a small sample of skin and see the differences under a microscope.

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    And if they're human and fail the test?
    – Möoz
    Oct 12, 2017 at 10:33
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    You mean the psych test, or a microscope test? I think it's easier to fail a psych test. :) Oct 13, 2017 at 11:10
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    @Mooz - Then they're human
    – Valorum
    Oct 2, 2021 at 8:55

Why not put a frigging Wallace Industries sign on their foreheads and if people don't like this aesthetically, then make it invisible in normal light. Why not put an explosive charge in their heads that detonates whenever the owner says the key word?

There are a million ways to at least make them reliably identifiable and probably to defend ourselves from them. You give them a key word that has to be periodically spoken to prevent a charge from going off and another key word, in case they hold you in tied up to a chair and tortured that you can utter that makes the gram of TNT next to their heart maybe explode and you don't even tell the replicant it's there. Why wouldn't these ideas protect humans from replicants?

SO THE ANSWER to the question is it is a plot contrivance: the makers of replicants deliberately wanted them to seem human, maybe even wanted them to be unidentifiable so they could be used to infiltrate enemy barracks. They are hard to identify because every way of identifying them was considered by Tyrell and circumvented so that all that is available is a V-K test that takes an hour to administer and may result in the test giver being offed.

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    This doesn't answer the question asked in any meaningful way
    – Valorum
    Oct 2, 2021 at 7:57
  • @valorumL sure it does -- the implicit answer within my post is because the writer wanted it to be hard to identify replicants and so made them almost unidentifiable but there is no good reason not to make them blue or plant explosives in their chests to render them harmless.
    – releseabe
    Oct 2, 2021 at 8:00
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    Meta answers are not something that makes a good answer. Obviously they wrote it that way. If you're determined to write a meta answer, a vaguely interesting one would at least focus on the thought process behind why they wrote it that way.
    – Valorum
    Oct 2, 2021 at 8:03
  • @Valorum: I modified my answer. They wanted them to be unidentifiable because this may have served Tyrell's purposes. If he was as big an ahole as Nianader Wallace, he probably planned to infiltrate other companies and governments with what he thought were hidden and obedient (to him) killers. I am pretty sure I am answering not only why they were hard to detect but also why Tyrell wanted them to be hard to detect.
    – releseabe
    Oct 2, 2021 at 8:08
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    "More human than human is our motto". If there was a marking of some kind that made them stand out, even if it's invisible to ambient light, i think they wouldn't look more human than human.
    – Clockwork
    Oct 2, 2021 at 11:58

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