Does anyone know the meaning of "eight diseases" in poetry?

Rhythm Disease The theory of poetic creation put forward by Shen Yue and Zhou Qing in the Southern Qi Dynasty during the Southern and Northern Dynasties. It mainly includes two aspects. First, the establishment and application of four tones; The second is to point out the morbid criminals of poetic meter. Shen Yue and others divided the unique tones in Chinese phonetics into four categories: flat, rising, falling and entering, and applied this division to poetic forms. There are many phenomena in the application, which classify Shen Yue and others as pathological criminals and call them "acoustic diseases". That is, flat head, upper tail, bee waist and crane knee. Later generations also exhibited big rhyme, small rhyme, side button and positive button. * * * There are eight kinds. Known as "four sounds and eight diseases."