What is it be human?

It's probably pretty obvious that the question of what it is to be human is one of my favorite themes. I enjoy science fiction and horror so much because the definition of humanity is so often challenged. Blade Runner will always be a favorite movie of mine for that reason.

Although Zomblieland is a straight-up comedy, I did end up reflecting a bit on what it is to be human after watching it. In the movie, Tallahasse achieves a sense of "flow" while slaughtering zombies. It's his talent and he enjoys every zombie head he's busted and every zombie belly he's punctured. What always strikes me as a little disturbing is how much I enjoy seeing those zombies blown away. There's some kind of catharsis in seeing something inhuman destroyed in a wildly spectacular way.

Seeing humans devoured by zombies in an equally spectacular way at the beginning of the movie was, in contrast, extremely disturbing. Both zombies and humans are played by human actors. Both run madly around. It's true the zombies regurgitate black goo, shuffle and have green skin, but they look human. What marks them for me as inhuman? Is is the fact that they eat humans? I don't think that means I'd enjoy the killing of cannibals. Is it because they look half dead? I don't think it follows that I'd take pleasure in seeing the death of the mortally wounded in a hospital.