What are Niu Niu and Xiao Mei?

It comes from a joke. This stem comes from a joke. Once Xiaomei lost her temper with Niu Niu and said, "I hate you!" " Niu Niu thought of a new stalk. He said, "Do you hate me? Then I will become Niu Niu and you will become Xiaomei. See who hates who! " Xiaomei also smiled, and their quarrel ended like this. From that day on, Xiaomei's love in Niu Niu became more stable. Every day they laughed and said, "I hate you, so I became Niu Niu."