Poisonous snakes

A passage from Can Xue's "The Child Who Raised Poisonous Snakes," as translated by Ronald R. Janssen and Jian Zhang:

"Now I don't need a place to raise snakes," Sha-yuan answered. "They are in my belly. They don't stay inside all the time, of course. They come out whenever I want them to. The little flowery snake is my favorite."

...

When I asked him quietly about the snakes, he said they were still in his belly. But he had learned how to adjust, so that even running and doing the high jump would not cause him any harm. Sometimes, having snakes in his belly was even beneficial to his health...

I wonder what the poisonous snakes represent. They're aggressive and damaging, they bite and hurt other children. They live inside him. Sometimes they hurt him. He claims sometimes they're "beneficial to his health," though the protagonist expresses doubt. I feel like it's on the tip of my tongue...