A video camera films the reflection sent back from a light directed at the reflective wall behind you. If you touch the two white walls with your hand, you will notice that one of them is perfectly smooth and the other one, where the image is being projected, is rough. It is the smooth wall that reflects the light provided by the lamp by the rough wall. When you enter the room and move around, your body blocks the reflective wall. The light can no longer be reflected from the light to the video camera. The shadowy figure representing your body is therefore black. The image from the camera is then fed into a computer where it is manipulated before being projected on the screen in front of you. Like a ripple effect in still water.