Hot and Cold is a tactile, heat-sensory illusion, in which touching a combination of warm and cool coils produces the sensation of “hot.” There are different kinds of nerve cells, or receptors, in your skin. Some of these cells are responsible for your perception of pain; others respond to touch; still others are sensitive to temperature—some to warmth and some to cold. This illusion happens because some of the nerve pathways that run from your skin to your brain are shared by different kinds of sensors. When you touch the center section of the coils, which are alternately warm and cold, your brain gets two conflicting messages.