While writing the word "birthday", the copper coin drew a turtle with a snake around it.

Xuanwu, also called Xuanming, is a combination of tortoise and snake. It is the water god, living in Beihai, and the tortoise lives long. Xuan Ming has become a symbol of immortality, and the underworld is also in the north, so it is the god of the north. Xuanwu is different from other three spirits because it can ask divination in the underworld. It is called the God of Tian Xuan and the "Zhenwu Emperor", and it is the god worshipped by Taoism.