Not long ago, I met a mentally ill person who asked me a question that made me think for a long time. He said that when he speaks now, others can't understand him, not even his attending physician. Then he asked me: why do you think there were only 400 million people in China at the beginning of the founding of the country, but now there are 1.4 billion? If reincarnation really exists, where do these additional people come from? Just as I was about to answer, he continued. He said: do you ever feel this way? Sometimes when you talk to others, no matter how you explain, they just can't understand. They are not bad people, but they really don't know they are wrong and think everything they do is right. Then he suddenly leaned in closer and asked me in a particularly strange tone: have you ever thought that oxygen is actually toxic? This poison just prevents you from living to a hundred. Then he asked me: do you think I am mentally ill? At that moment, I was stunned and fell into deep thought. His questions were so bizarre that I was left bewildered. I thought for a long time and then asked him: what does this have to do with the increase in population? He snorted and said softly: have you ever thought that many of the people we see now are not really human at all.