Shark
Sharks have tiny holes all over the shark's snout, especially between the eye and the tip of the snout. In them are nerve receptors which are called the ampullae of Lorenzini. p23 They can sense electricity in the water. Animals in the water give off electricity: every time an animal's heart beats or it moves, tiny currents of electricity are made. These tiny electric currents make signals that travel through water and get sensed. Sharks may use this sense when they catch their prey, even more than they use their sight.