Kanizsa triangle. This image appears to depict a solid triangle overlaying another triangle. This triangle looks brighter than the background. In fact there is no triangle. In reality there are just three cutaway triangles and three arrow shapes. Illusory contours are created to surround a shape that is not there. This is probably caused by our brain interpreting our surroundings and trying to extrapolate from fragmentary data. However, there is still no definitive explanation for this phenomenon.