Anticipation

'Anticipation' is a principle in animation that pays attention to the moment preceding a main action. For instance, a baseball player winding himself up to throw a ball: anticipation would be considered the actions leading to the ball leaving his hand.

Consider in which direction the main action is about to go, and as a general rule the anticipation will be in the opposite direction. In the case of throwing a baseball, we would expect an arm to go back behind the body before being thrust forward. An athlete preparing for a long jump may lean back before breaking into a sprint, and a sprinter will crouch to create more spring on take-off. A jump would always come after the bending of knees. Imagine these actions unfolding without anticipation and it is clear how essential the preamble is. Noticing and emphasising this can create more realistic action and ultimately can give more power to the animation.

This frog demonstrates the classic cartoony snap of winding up before shooting off in the opposite direction.

Here's a much more subtle example showing anticipation before a gentle stroll.

There is a degree of clarity that anticipation gives the audience for what they are seeing. There are many ways to telegraph what is about to come by showing a minor action we all recognise. Think how often small moments in life always come with a little build-up. If someone were about to sneeze you can see it coming from a mile off, with a huffing and puffing; if someone sneezes with no anticipation it would be too sudden and plain odd.

Of course, you could play around with convention for the sake of doing something unexpected. If a character looks in one direction to direct the audience to anticipate something on that side of the screen, then something could happen as a surprise i.e. hitting them on the back of the head.

Watch how the extreme anticipation here gives greater impact on the hit. If the attacker is coiled up in anticipation of releasing that power, we as the viewer recognise that the energy has to go somewhere, and so we feel it on the strike.

It's up to you how much you wish to exaggerate any given action. It will depend on the tone of the scene, but keep an eye out for where anticipation would be necessary and could potentially enhance any action you're showing.