A while ago, I met a person with a mental illness who asked me a question that made me think for a long time. He said that when he speaks now, others cannot understand him, not even his attending physician. Then he asked me: Why do you think there were only 400 million people at the beginning of the founding of China, but now there are 1.4 billion? If reincarnation really exists, where do these additional people come from? I was about to answer when he continued. He said: Do you ever feel this way? Sometimes when you talk to others, no matter how you explain, they just cannot understand. They are not bad people, but they really do not know they are wrong and think everything they do is right. Then he suddenly leaned his face closer and asked me in a particularly strange tone: Have you ever thought that oxygen is actually toxic? This kind of poison just prevents you from living to a hundred years old. Then he asked me: Do you think I have a mental illness? At that moment, I was taken aback and fell into contemplation. His questions were too strange, leaving me confused. I thought for a long time and then asked him: What does this have to do with the increase in population? He snorted and quietly said: Have you ever thought that many of the people we see now are not really human.