Fish don't sleep in the same way that we do, but they have active and
inactive periods. Some sharks (like the nurse shark) have been observed resting
motionless on the sea floor. Others have to keep moving in order to breathe.
When some sharks (like the Great White or the Gray Reef shark) turn
aggressive prior to an attack, they arch their back and throw back their head.
This places their mouth in a better position for taking a big bite. They also
move their tail more acutely (probably in preparation for a chase).
Sharks do not normally attack people, and only about 25 species of sharks
are known to attack people. Sharks attack fewer than 100 people each year. Many
more people are killed by bees or lightning.
The sharks that are the most dangerous to people are the great white shark, the
tiger shark, the bull shark, and the oceanic whitetip shark. The bull shark
is the most frequent attacker of people as it swims in very shallow waters where
people swim and is a very plentiful shark. Some of the other sharks that are
known to have attacked people include the gray shark, blue shark, hammerhead
shark, mako shark, nurse shark, lemon shark, blacktip reef shark, wobbegongs,
sandtiger, spitting sharks, and the porbeagle. Some people believe that sharks
mistake people (especially people swimming on surf boards) for seals and sea
lions, some of their favorite foods.