How did Hong Haier know who the Monkey King really was?

First of all, the Monkey King said that Tang Priest was released, and Hong Haier became suspicious. Then Hong Haier asked the Monkey King why I didn't bring a present for my birthday. The Monkey King said he was in no hurry to bring it, and he would send it another day, so he got it.

Hong Haier asked Xiaoyao when he saw Niu Wangmo. Xiaoyao said he met him halfway. At this moment, Hong Haier is still not sure whether this NiuWangMo is true or not.

Later the Monkey King said the word "seventy-two changes". Can't his father change 72? In order to further confirm the authenticity of Niu, Hong Haier asked about his date of birth, because Niu always talked about Hong Haier's birthday on weekdays, and the Monkey King was betrayed.

Extended data:

It happened in the 40th time. the Monkey King in The Journey to the West became Niu Wangmo and was discovered by Hong Haier.

The 40th lecture is mainly about: Hon Hai's longitudinal wind scared the Tang Priest away. Wukong learned that Hong Haier was the son of his sworn brother Niu Wangmo 500 years ago, and wanted to ask him to return it to his master. Hong Haier didn't believe what Wukong said. He blew smoke from his nose and mouth and burned Wukong and Bajie. Brother Longwang was asked to spray water on Hon Hai 'er and almost killed Wukong in fireworks.

Bajie invited Guanyin, but the monster pretended to be Guanyin and made money in the cave. When Wukong became Niu Wangmo, he was questioned by Hong Haier and threw himself into the South China Sea, begging Guanyin to surrender to Hong Haier.

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