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At first when I saw the guy not get hurt, I assumed this was a simulated / virtual reality world. Then as the episode goes on it's shown that it's a real, physical place, with artificially intelligent robots. I sort of get the idea that the AI's programming keeps them from harming living things, but if, like in that case, the robots don't know the difference, how can they know not to kill them? They certainly have no qualms about killing each-other?
And then, when the robot shoots the "bad guy" (not sure about character names yet) with the same gun he just "killed" 2 other robots with (the ones who killed the girl's parents), how is it that the guy is immune?
I'm looking for an overall explanation of how the system of not hurting some things (flies, humans, etc) whilst hurting other things (other robots) works, and how their bullets just have no effect of living things, but hurt other robots.