Bowing your head means nodding. Bowing one's head in an instant refers to a person's humble obedience. Head and fingers refer to the whole body with limb parts. Nodding one's head and lowering one's eyebrows is also a gesture of bowing and modesty.

Low eyebrows, eyebrows pointing to the head, low eyebrows pointing to the head.

A moment means nodding, and a moment of nodding is like bowing your head.