This will only make sense to you if you have ever seen documentaries on fish from deep under the sea, where it is so deep that no sunshine penetrates the water. Otherwise you'll just think me mad! Anyway, these fish have to rely on fabulous lighting displays, from bioluminescence, which are created by chemical reactions inside their bodies, to be seen by their mates and enemies……. How does this relate to Cairo? You should see the feluccas and small boats which cruise the Nile at night!