Animation 2nd Basic is Anticipation.

Anticipation is used to prepare the audience for an action, and to make the action appear more realistic. A dancer jumping off the floor has to bend his knees first; a golfer making a swing has to swing the club back first. The technique can also be used for less physical actions, such as a character looking off-screen to anticipate someone's arrival, or attention focusing on an object that a character is about to pick up.For special effect, anticipation can also be omitted in cases where it is expected. The resulting sense of anticlimax will produce a feeling of surprise in the viewer, and can often add comedy to a scene.This is often referred to as a 'surprise gag'