Some neurologists swear by “mirror neurons,” a subset of neurons that fire when we observe someone else doing or feeling something as if it was us — they believe that the neurons provide an evolutionary benefit by endowing us with the empathy required to function in a group. Not everyone agrees.
There are psychologists who suggest that if we see a characters as having human motivations, we’re programmed to decide if we like and care about them or not, or if they make us furious or scare us.
And, of course, we can’t discount the purely manipulative power of a movie soundtrack. Artful soundtrack composers know how to work our feelings with music, even if no one really understands the mechanism that makes music so unbelievably effective at doing so — it’s another topic for another day.