Animation is a dynamic medium in which images or objects are manipulated to appear as moving images. Commonly the effect of animation is achieved by a rapid succession of sequential images that minimally differ from each other. The illusion—as in motion pictures in general—is thought to rely on the phi phenomenon and beta movement, but the exact causes are still uncertain. The physical movement of image parts through simple mechanics in for instance the moving images in magic lantern shows can also be considered animation. Mechanical animation of actual robotic devices is known as animatronics.