There are methods to observe people and undoubtedly recognise the manner how they think and their character. We say that the Self closely listen the heart, observe him, that he can be seen and understood as an image in a mirror. The one who have a disturbed heart can be quickly be the victim of others. That’s why the shinobi use this technique and can follow everywhere the heart of the adversary and penetrate him. This is the basics technique of the shinobi.

Shôninki – Natori Masazumi