Inspired by Zhuangzi’s philosophical question - how do people understand reality.  If the dream is real enough, it is difficult for people to know that they are dreaming.  But it could also be a lucid dream about the unity of nature and man.

The story of  Zhuangzi dreamed one day that he had turned into a butterfly.  After waking up, he found that he was still Zhuangzi, so he didn't know whether he had become Zhuangzi's butterfly or Zhuangzi who had become a butterfly in his dream.