Secondary animation
Secondary animation also known as secondary motion, is used to refer to flat motions that are generated as a reaction to the movement of primary motion by a character. It is significant in animation because it amplifies the character's motion via effects that appear to be driven by the motion, i.e. it makes the character's motion seem natural. Examples of secondary motion include the rippling of water, swish of a cloak, or jiggle of body parts when a person is moving. These passive effects have many degrees of freedom, and complex interactions with characters, thus making  them hard to animate by hand (hand animation), or via computer software. Techniques. Creating a second motion requires using a technique called coupling that combines simulations of individual objects allowing them to interact together to produce secondary motion. The coupling can be divided into three categories: two-way coupled, one-way coupled, and hybrid.