In one, the only things visible are things that are standing still. The effect is that of long-exposure photography, except that the image is truly live, changing subtly at every video frame. People that are moving are blurs or fogs across the image. People that are still are seen clearly. The second process is the conceptual inverse of the first.
People are only visible if they are in motion.
They float as outlines of themselves in a dimensionless black void, and disappear again as soon as they are still. The two images are projected with the first image beside the second, and with the second image flipped horizontally to mirror the first image. There is the sound of a watch, a clock, a heartbeat and light breathing. When the images are in this state, they are mutually exclusive. A person cannot exist in both images at once.