Tango dance (1) is to shake the head when the closed position changes to the pp position. (2) It is to shake the head on the second fastest beat of the music.

The legend of sudden head-shaking in tango dance: It tells that a sailor returned from the sea and danced tango with his long-lost girlfriend. As he was dancing, the sailor noticed that his girlfriend kept turning her head, so he suddenly turned around and found that his girlfriend was looking at his new partner, and he suddenly became jealous. So later on, there was the sudden head-shaking movement in tango.