Various sharks have small black dots along their head, face and jaw, which looks like they forgot to shave. In fact these black dots are small pores which lead to little jelly filled canals. The jelly is ultra conductive and the voltage at the pore is measured against the voltage within the jelly. This voltage difference gives the shark an extremely sensitive detection to electrical fields in water, more so than any other animal. The bonnethead shark can detect sensitivities as low as 1 nV/cm (1/1,000,000,000 of a volt measured in a centimeter-long ampulla). For comparison that’s similar to the electrical field generated by an AA battery connected to electrodes about 10,000 miles, roughly 5 million times more sensitive than anything a human could detect. Since living creatures produce electrical fields via muscle contractions and movement, the shark can easily find prey with this method, even flounder and other fish who bury themselves under sand. Additionally, wounded prey thrash more and bleed into the water releasing charged electrolytes which creates an electrical field which can be as much as 3 times stronger than uninjured prey, therefor in bloody or dark waters the shark has a clear advantage.
5 - Ultraviolet World
Most insects, some birds and a few reptiles can see into the near Ultraviolet which is a shorter wavelength than the light visible to humans. Bees are reputed to be able to see ultraviolet light very well which helps them find and chose which flowers to collect pollen from. Recently scientists were amazed to discover a whole new world, hidden in plain sight, when they took special ultraviolet photographs of common plants and flowers. This revealed beautiful patterns which are undetectable to the human eye. Likewise many birds and butterflies have patterns on their plumage or wings only observable by ultraviolet.