What do you mean, eat with your mouth open

In the old society, performing Chinese opera, Quyi and other occupations were called eating with your mouth open. According to the query of Modern Chinese Dictionary, the explanation of Zhangkoufan is: In the old society, performing opera and folk art was called eating Zhangkoufan. Modern Chinese Dictionary is the first standardized modern Chinese dictionary in China, that is, Putonghua Dictionary. The book was compiled by the dictionary editing room of the Institute of Linguistics, Chinese Academy of Social Sciences, with Lv Shuxiang and Ding Shengshu presiding over the work successively.