He could see clearly how the strength of his citta began to develop and how he attained the foundation of samadhi firmly because of his having gained that nimitta, which acted like a grind-stone to sharpen up his sati and pañña all the time. He went on in this way until he was able to get the skeleton image of that nimitta to stay within his own body, so that his body and the skeleton became identified as one, and this went on until he had no doubt as to where this skeleton came from and who became this skeleton.