When a light moves quickly, it appears as a streak. Over a century ago, while swinging a lantern, Professor Lardner asked: "Do you really believe the lantern is in all those places at once?" The brain remembers an image for 1/10 of a second. This delayed response is called persistence of vision and explains how the images of movies, videos, and flip-books seem to blend together. The Persistence of Vision Fan shows this concept perfectly with two spinning fans covered in colorful LEDs that flicker at different speeds, giving the illusion of streams of light instead of individual dots. The Zoetrope is the best known of several animation toys which were invented in the 19th century, a time when people first discovered ways to make still pictures move.