Philosophical Zombie
The ‘duck theory’ is a possible (though not always accepted) answer to this - if it looks like a duck, walks like a duck, quacks like a duck, etc, then it is a duck.
This approach defines Mark as a human (as he’s indistinguishable from a human), and states that p-zombies are impossible, that they’re equal to people.
https://philosophy.stackexchange.com/a/11196
but I think right now that Philosophical zombies will be possible.