Have someone throw a ball or other object to you while you are standing on one foot (you can also bounce a ball off a wall if you're training alone). (hardgainermusclebuilding.com)
Then you discover that the copyright owner objects to you using this video. (rocketlawyer.com)
Focusing is surprisingly quick, especially when you move from a close - up object to something far away and vice versa. (sammobile.com)