Are Nuns Allowed to Drop Pianos on Zombies?

One of the many serious questions raised by the movie 'Zombieland'. Are nuns--- and women religious in general--- allowed to drop pianos on zombies?

 Now, the Sister Cynthia Knickerbocker depicted in the clip is clearly not a nun--- a cloistered woman religious--- because she's out of uniform. A cloistered nun has to remain within the enclosure unless she has her superior's permission to leave. Though not intended for zombie protection, I'd imagine those enclosures are pretty zombie-proof. So for the cloistered nun the issue would be this: would she have any zombies to kill within the convent?

 The kind of religious sisters that teach in schools or nurse in hospitals, and who these days often don't wear habits, are perfectly free to leave the convent grounds. But are they allowed to kill zombies once they get there? Catholics, in and out of convents, are required to respect human life from conception until natural death. Zombies have already been through their natural death, that's true. But Lazarus in the Bible died, was in the tomb awhile, and Jesus raised him. I don't think it would have been OK for some one to kill Lazarus based on the fact that he was already dead once.

The question is whether the apparent life of the zombie is human life. If it is not--- if the soul of the person has fully departed and the corpse is just walking around, animated by a virus, an alien entity, an evil spirit, or whatever, killing--- or re-killing--- is justified. Zombies are just a pest, like plague rats, that we can kill for the safety of others.

 The problem is, how do you prove the soul has left? How do you know that the zombified person isn't just suffering from brain damage which left him violent? And how does that research get done in the middle of a zombie apocalypse? Without that proof, Catholics, whether or not they are consecrated religious, can't just kill zombies because they are zombies. Each zombie kill has to be, individually, a self-defense situation. Of course, with zombies, most situations quickly degenerate into legit self-defense situations. But piano-dropping? That's premeditated, that's trapping a Z before you are sure he's out to kill you. Sister Cynthia Knickerbocker's probably gonna have to say three Hail Marys or something.