Shivering is an involuntary, and rapid body movement typically associated with being cold, or afraid. Shivering tends to be characterized by wavy lines, or thin irregular scribbles along the contour of a character.

Shivering is sometimes context dependent. If the movement lines look more like well defined spiky lines, trembling is likely the better tag to use. If the lines are smooth and curved, this is likely neither trembling, or shivering, but still may fall under shaking, or just motion outline.