The Bull Shark is a species of shark found in both fresh and salt water worldwide. While it spends most of its life in the ocean, it is capable of swimming in freshwater for long periods of time. This is due to a "salt exchange system," which prevents too much salt from leaving its blood cells, which would kill most other sharks. Its name comes from its behavior of charging into its prey like a bull. It has attacked humans before and is considered one of the more dangerous sharks, particularly due to its ability to enter freshwater.