As recently as the late-1800s, people had no idea how horses ran. To the general public’s astonishment, Eadweard Muybridge revealed that at a point during a single “revolution,” all of a horse’s four legs hover over the ground.
This was demonstrated through stop-motion photography, which has been animated here. Muybridge made an animated projection of the idea afterwards, possibly influencing Edison’s invention of the precursor to the motion picture camera.
Source: Wikipedia – Eadweard Muybridge, Wikipedia – Sallie Gardner at a Gallop, UT Austin’s Harry Ransom Center Permanent Collection