Answer: a shark's sense of smell comes in handy in this situation. sharks have noses that arent used to breathe but to smell (they have a gill system for breathing) the shark can smell the blood from up to a quarter-mile away.
Explanation: sharks also pick up on minute electrical impulses using organs they have called Ampullae of Lorenzini. these organs are made of tiny hairs that are hidden in pores on the underside of their head
