13160_13236_natgeo
A silhouette of a boxer behind a hazy red screen. An infrared image of a hand. An image of a body of only muscles pulling on an imagined rope. X-ray of a shoulder as it lifts an arm. Infrared image of a mouth taking a sip of coffee. An internal camera snaking through an artery. An X-ray of a head taking a bite of food. Red blood cells flowing through an artery followed by an ECU of a pupil contracting. An X-ray of foot bending followed by a track runner starting a race. ECU of a live heart beating. ECU of a heat valve opening inside the heart. Red blood cells, followed by white blood cells and sperm. Cells divide, a uterus in the womb, and a gymnast holds themselves upside-down on the hoops.