Secondary animation

Secondary animation (or secondary motion) is the motion derived from primary motion, much like a ripple or jiggle of different parts of the body when a person walks. In Rocky, Sylvester Stallone is reported to have insisted that he really be punched to get the secondary motion correct, with his face distorted and rippling from the blow on the opposite side, and sweat flying off from the force of the blow.

In animation, movement can look stiff and mechanical if the reactive bouncing of flesh and clothing isn't correct. This motion has a displacement and time delay from the original motion making it complex to calculate. Slower motion capture systems that require smoothing often look "creepy" from the effects of smoothed motion, which causes overly smoothed secondary motion making gestures float rather than reflect natural motion.