Secondary Action is the finishing touch on animation. It’s the small details that really make an animation come to life. You might not even notice it initially, unless someone or something explicitly points it out!
In this animation, I made every body part move, even if it's just the very slightest. The shoulders rise and fall, the hands sway, and the hips go from side to side. Since it is armature animation, each bone moves in relation to other bones. For example, when the character moves downward, his knees bend.
My Finished Example: