Prof. Harald Giessen performs the equivalent of an optical cloaking experiment in an aquarium (water with sugar solution) with a green laser beam. This experiment has long been known in introductory physics and optics classes and demonstrates Fermat's principle. Light travels always the fastest path. The sugar solution has a higher refractive index and sinks to the bottom of the aquarium, whereas the less dense water is above. The green laser beam at 532 nm is refracted accordingly, being in principle able to travel around an object.