Have you ever wondered if what you're seeing is really it makes itself to be? Everyday you probably experience or see the same events on a regular basis. You become so used to something that it becomes second nature that you don't even have to think about it. Take for example gravity. You know that when you throw something or slide down a slide that the object will move towards ground until making contact with it or something on it. This video creates an interesting perception of what we would normally expect.
When you first see the constructed object, it appears to be a ramp of some sort that goes up and down. However, once the person starts placing toy balls at what appears to be the bottom of the ramp, the balls seem to travel up the ramp! You probably were not expecting that, were you?
But how can this be? This event went against to what you have believed in. At around 0:27 seconds into the video, the camera rotates around the object to show that it was not what it was initially made out to be. But why did you believe it was a ramp that went up? You see you have already developed a perceptual set that the ramp went up and the balls would just roll down it when placed on it. This is an example of top-down processing in which your expectations of things will affect the way things are perceived.