In my Zen training days, the encountering of Daoist master Sanfeng Zhang‘s manuscript “Rootless Tree"(Wu Gen Shu Ci 無根樹詞) is one of my favorite classic work. Besides the opening alarming words describing life is just like unleashed boat, the other sentence of my favorite quote is “you shall swallow the spirits of sun and moon, to replace the dusty old internal you."
In China golden crow is the symbol of sun, and rabbit represents the moon. Lead caldron represents truth, boiling the body to connect the universe. When Chin dynasty author I-min Liu explains about it, he said:
Lead caldron is the truth (machine) because we could replace the old with the new, and enable us to reach the fairy status, so we call it with the shape-metaphor as caldron.
The liver of the crow is blue, and it represent the spirit of the sun. It also represent the spiritually you. The soul of the rabbit is in white, and the spirit of the moon, represent the truth affection. Swallowing them then you make the spirit connects with the affection and turn into one. Round and shining, naked and returning to the original nature, getting rid of all the culture things. Then burn out all the fame / gain / grace / love, only left with the completed emptiness.