Immersive virtual reality is the research tool those of us who study human perception and action have been waiting for, because it enables us to perform rigorous experimental studies of natural behaviour. First off, it allows us to easily manipulate realistic visual environments while collecting continuous measures of ongoing behaviour. But its greater potential lies in the ability to test psychological theories by manipulating the world in impossible ways. I will describe several studies in which we break the laws of physics and optics to investigate some interesting visual-motor control...