The hair swinging creates the sense of being suddenly slapped. Draw the neck a little on the long side when the head swings directly to the side. This works for both serious scenes and comedy.
A downward diagonal slap creates a morę serious mood. Expressions facing downward ephasize the 'deep meaning' of the scene. 3%,
For violent slaps, the character gets mowed down to one side while the direction of the face and body remain facing forward. This is slightly different from standard punches and kicks.
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