Throughout its life a shark grows new teeth to replace those it has lost and to keep pace with the growth of its body. The shark has senses specially adapted for the animal's life underwater. Smell is a shark's most acute sense. Approximately 70 percent of the shark's brain is used for olfactory functions. Experiments have shown that sharks can detect prey solely by smell, and the hungrier the shark, the less stimulant needed to elicit a reaction.
Sharks are sensitive to light and can detect certain objects even in murky water.
Some have a tapetum lucidum, a mirrorlike layer under the retina that reflects incoming light and increases the amount of light available to the eye. Sharks do have ears, but the role of hearing in the shark's location of prey is not well understood. A shark can detect sound waves and disturbances in the water with its lateral line, or lateralis, system. This is a series of thin canals, filled with water, that runs along the animal's side. The canals are attached to nerves that send signals to the shark's brain.