Sharks possess an amazing sense called electroreception. The ability to sense tiny electrical currents is outside of our range of abilities and may not seem all that useful. But I think you'll be surprised at how remarkably handy this sense can be if you are a shark searching for food in the vast ocean realms.
The electro-sensory system of a shark is so sensitive that it can detect the tiny electrical currents generated by the muscles of a fish swimming nearby, a great advantage for those trying to find prey in the pitch-black. This ability would be like a magic sixth sense to us, considering that a shark can detect the electrical signals given off by the beating of a fish’s heart (or human’s heart for that matter).
Consider the implications! As soon as you jump into the ocean, every shark in the vicinity knows you are there. There’s no hiding behind a boat or chunk of coral. If your heart is beating or your muscles are twitching, sharks will sense the electrical current.
Sharks have by far the highest level of electrical sensitivity of any animal on the planet.
Electroreception is based on a system of sensory organs called the ampullae of Lorenzini (see my article to learn more).
Electroreceptor pores on the snout of a Leopard Shark. Photo by Albert Kok on Wikimedia CC-by-03
The electrical sensitivity of a shark is equivalent to being able to detect the electric field of a flashlight battery connected to electrodes placed 10,000 miles (16,000 kilometres) apart in the ocean. Seems like a stretch, doesn’t it! Believe me, this is based on extensive research.