When I see you in pain, I feel your pain and my face automatically expresses this pain. What's more, you can see by my expression that I share your pain, and you are comforted by the knowledge someone else shares your pain. You are responding to my response to you.
Such interactions are a feature of many aspects of everyday life. They come to the fore when people play music. So in an experiment that got two people to tap a simple beat together, you might expect a leader and a follower to emerge, with the leader trying to maintain the beat, while the follower synchronises with the leader. But when each person could only hear the other, but not him or herself, no leader emerged. Both players became followers, continually and mutually adjusting their taps to each other.
Capgras sufferers recognize their image but do not recognize it as belonging to them.
They have no self.
This is because of damage to communication between Amygdala and frontal cortex responsible for face recognition.
They act like image recognition devices for detecting number plates.
But the thing that makes us human is the emotion we attach to this image.