saccade

A rapid movement of the eye (either voluntary or involuntary) from one focus to another. (Often described as a jerky movement, but this word denotes all such quick eye movements, which happen continually, not just exaggerated or weird ones, and not nystagmus.)

The act of checking a horse quickly with a single strong pull of the reins.

(rare) Any sudden jerking movement.

The sounding of two violin strings together by using a sudden strong pressure of the bow.

To make a rapid jerking movement to focus elsewhere.