I believe the messages for stealing should be changed to make more sense. After you steal from a monster and/or it notices your attempt at pilfering, it says "Your attempt is prevented" and I think it should say "The monster stops you from pilfering it" or "You cannot steal from a monster more than once!" if that's the case.
Also, it should say, "You cannot steal from players!" instead of "You can only steal from NPC!"