When did Ava become human?

Rating: 10/10 (21 October 2015)

Excellent movie ... lately, my favorite movies are sci-fi stories that focus mainly on character development with having more questions than answers.
The character of Nathan was especially interesting, in that, I agreed with a lot of what he said ... how can he be the bad guy?
If Ava is the good guy, why did she leave Caleb?
If Caleb is the good guy, why was he abandoned by Ava?
The one scene that struck me as powerful was when Ava escaped and confronted Nathan physically and he smashed her arm. If you believe that human history shows that we are "born of violence" and "violent by nature" and, if this was the first moment that Ava experienced violence, then it's same moment she became human. Check out the look on her face ... the only time in the movie she showed doubt and uncertainty ... once again, human.