You can't fool a camera (1941)

This short starts out as a documentary. In a dramatization, Eadward Muybridge's photographic experiments prove that when a horse gallops, there are times when all four of the animal's feet are off the ground. We are then brought to the present, where MGM directors and their cinematographers are shown working on current productions. The film closes with closeups of the studio's major stars and a tribute to the studio's actors who have joined the armed forces.