Secondary actions add another layer of realism and quality to an animation. The secondary actions are the other limbs or objects moving along with the main action. They are not the follow-through actions, which are inanimate objects reacting to the main actions. They are the limbs that move, such as the character's arms swinging rhythmically back and forth when walking. He could nod in time to music while taking a stroll or blink or chew gum.