The eye can be compared to a camera. The incoming light is projected onto the retina, via the transparent cornea, pupil and eye lens. On the retina there are nerve cells that direct the light stimuli to the optic nerve. From there, all stimuli together are passed to the brain that composes an image of it. Not all animals perceive the world in the same colors. Some animals are able to perceive ultraviolet light, others lack the cells for certain colors. Some snake species can detect infrared radiation by heat-sensitive receptors in the skin of the head (Boa) or a groove under the nostril (Pit Viper). These receptors are comparable to the ones with which we humans perceive warmth. We don’t call them eyes, although there is probably a form of visualization, as snakes use them to find warm-blooded prey and are able to determine both distance and direction. So is what we think we see, the 'reality'?