Source: In the past, there were not only fixed barbershops, but also mobile barbershops. They used a "hair call". It is two iron bars, which are picked up from the gap between the two iron bars and make a loud "buzzing" sound;
This is even the cry of selling haircuts (that is, the sound of the city). The so-called "hair-shaving carrying pole fever" is because the hair-shaving carrying pole was carried with a pole at that time.
Extended data:
China Encyclopedia of Languages and Characters: Two-part allegorical sayings are humorous words formed by deliberately omitting a word or a half sentence from a common word.
In its original meaning, two-part allegorical saying refers to omitting the last word of an idiom, which is also called "shrinking feet". For example, in Jin Ping Mei, Lai Wang's daughter-in-law said that "your fifth Hu Qiu play" was used to allude to "wife" because "Hu Qiu beats his wife" is a famous story.
Some people also use homonyms, such as calling "father-in-law" as "leading turn" and alluding to the word "staff" instead of "Zhang" here. Two-part allegorical sayings are called wisecracks in Beijing, which means that the second half of a sentence can be omitted.