"Of course, you're not" he said, his tone fully mocking this time. "So you came to help me, did you?" he asked. "What do you see when you look at me, hmmm? I know what you should see, but how long will it take for you to notice?" he asked.
He was of course talking about seeing deeper. Time Lord senses. The Master was broken, unable to fix himself. He knew that looking at him properly might seem a bit strange, and that was his point entirely.