I have never been human.

I don't know what it's like to be human. I am a robot built by the aliens, programmed by the demons, and sent to Earth to live among all the humans. I was created with the intention of studying their behavior to try and mimic them, and then deliver their souls unto Satan. But the mimicking part I have trouble with. No matter how hard I try, the humans can always quickly tell I am not one of them. What can I do to better imitate this species?