ninjas are the human equivalent of nightscales. They have the uncanny ability to turn invisible.The photo below is of a forest full of ninjas. You can tell it's full of ninjas by the fact that you cannot see any ninjas at all. If you can see them, they are not ninjas. They are people who jump around shouting 'hyaa' and hitting things with sticks. Ninjas, on the other hand, prefer to hide and then kill someone without anyone noticing. If it's a really successful ninja, sometimes the person being killed doesn't even notice, and continues on for a while (usually about two weeks) as a confused ghost.