Philosophical zombies that is.
Summary provided by Wikipedia
a hypothetical being that is indistinguishable from a normal human being except that it lacks conscious experience, qualia, or sentience. When a zombie is poked with a sharp object, for example, it does not feel any pain. However, it behaves exactly as if it does feel pain (it may say "ouch" and recoil from the stimulus), but it does not actually have the experience of pain as a putative 'normal' person does.
P-zombies are a reoccurring topic in one of the books that I am currently reading. What are your thoughts? Could such a creature really exist? What test could we devise to distinguish between an actual conscious being and a zombie (if any)?