From his perspective, this is getting away with it, and he will definitely try it again. Only next time, he'll be more careful. This guy is a psychopath. Everything he says is untrue, and he knows it. He doesn't give one shit about being truthful or even appearing to be. In his morality, there is no truth, and the only morality is whatever you can get away with.

He could be conditioned like an animal if he was made to suffer much more, but at that point, you're breaking the law.

This is the big problem with people like this. Short of things like high-security prisons and the like (and sometimes even in those cases), pretty much everything in human society is designed for people who respond psychologically like most people do. Choice have consequences, and desire to avoid those consequences effects deterrence. But for psychopaths, anything you survive, you "got away with", and you're free to try again. Only something like severe, agonizing pain, or the some kind of permanent injury, would really be an effective deterrent. A few slaps only mean, "Good try this time. Come back and try again, but be smarter next time." And he will.