I was lucky to be taught from an early age to tell a human from a clones and other unnatural "things".There are 10 basic male archetypes, female archetypes for genetic experiments are slightly more (it's because a male clone can be made into a "female" more easily than the other way around).
In the intelligence services here in Central Europe, it was part of the training to orientate in "them", it was taught in the times of the totalitarian regime. I don't know as it is now, but in my opinion the intelligence services have been infiltrated by clones too - I've been watching it for the last 20 years or so.
You can also easily recognize a cannibal by the muscle movements in the face and most of all by the mouth. After a long time, cannibals tend to have something that could be compared to muscle spasms, and it manifests itself most precisely in the face - hideous smile very similar to clowns.These convulsions begin to manifest most quickly after cannibalistic consume of the brain.

Kuru disease?