In their snout area sharks have pits, known as ampullae of Lorenzini, which detect the small electrical signals that all animals, including human beings, emit. This sense works best at close range and enables the shark to pinpoint an animal it may not even see in dark water. Metal objects also emit electrical pulses, a fact that may help explain why sharks sometimes attack boats, docks and steel cages. Specialized eyes enable the shark to see in dim light. Certain sharks, such as the reef and bull shark, have color vision that attracts them to bright orange and yellow hues.
Sharks are the only fish that have eyelids, termed nictitating membranes .
Several families, including the hammerheads, catsharks and smooth dogfish, possess these eyelids which roll up in the final seconds before it attacks, essentially leaving the shark blind. This action protects the shark's eyes from the flailing and scratching of its prey. Strangely, the aggressive great white shark lacks these nictitating membranes. Different species of sharks have different shapes and sizes of teeth specialized for the kinds of food that they eat, whether it be mammals, fish, crustaceans, or mollusks. Experts can identify a shark by the shape of its teeth.