Xu Chunliang told him that he went to He Tiantian Restaurant for a meal yesterday and happened to encounter Xiaosinan. At that time, he noticed that her eyeballs had a lot of gray spots. This usually indicates a parasitic infection in children.
Furthermore, Xiaosinan had mysteriously lost her speech for over a year. She had gone to the provincial capital to consult experts, undergone various examinations, but no results were found. The possibility of a brain tumor was ruled out, hence it was judged that her aphasia was caused by brain parasites.
Xiaosinan's living environment and her habit of liking cats and dogs increased the likelihood of infection. Taking all this into account, Xu Chunliang made his diagnosis. However, he didn't disclose all the bases for his diagnosis.
The "Manual of a Thousand Insects" specifically provides a clear diagnosis for Chun Si worms parasitizing humans. One indication is green light in the eyes at night.
