Around the world, there are only about 100 shark attacks on humans each year, ten of which prove fatal. But consider this, in the US alone, about 3 million people are bitten by dogs each year. Of these, 13 people die. If a shark bites you, says Dr. Clark, the reason is usually because it mistakes you for its natural food. For example, say you went underwater-fishing and saw a shark, you could be in trouble. The shark might go for the injured fish you had attacked and take a big bite of you at the same time. If you go into a shark's territory and threaten it, it might try to bite you. That's because sharks are territorial and tend to guard their territory. Like dogs, they protect the area that they think is their own.