Four modified infra-red sensors register the amount of movement occuring along the four sides of the image. Two cameras look across the image from opposite corners from floor level, registering movement only if someone in the installation steps onto the sand and begins reflecting the light of the projected image. When one enters the empty installation, a single video clip is playing out across the sand. The image creates the illusion of depth, the sand sinks underneath it. It is not clear that the 'screen' is sand.
People look around then reach surreptitiously down through the depth of the image to the dry sand.
Movement along a walkway is sensed by one of the infra-red sensors which sends an analog voltage roughly representative of the amount of movement. This signal causes a second image from the other disk to be dissolved in along the side where the movement took place. The second video clip is selected by a program from the possible clips on the disk based on the side of the frame where the current movement began. The new image usually contains shadows or reflections of people along the edge of the clip that is visible. One tends to interpret those reflections and shadows as the being generated by people actually in the room, either oneselves or others, rather than as being present in the image itself.