Do you understand the meaning of "knocking on the back"

Knocking on the back is a kind of massage, which beats the back rhythmically with the palm of your hand or empty fist and makes various sounds. Back tapping refers to a back tapping massage service, which makes the client relax muscles and relieve fatigue. There are many such services in saunas and bathhouses. However, in life, like the words "comrade" and "miss", the meaning has changed in use and evolved into another name for "erotic service" and "sexual service". For example, in hotels, saunas and other occasions, the so-called "back knocking service" provided by the opposite sex often refers to the latter. Of course, if your intention is just to knock on the back, knocking on the back is a normal service. Normal back knocking service is often called back knocking, which can be divided into "small back knocking", "middle back knocking" and "big back knocking". Its significance lies in providing different levels of services and charging different fees.