Fierce sharks usually move in the upper and middle oceans. It can swallow several small fish in one gulp, and it can also kill and eat bigger fish or other animals. Strangely, it never devours its inseparable companion, the guide fish. The guide fish is only about 30 cm long, with green back, white abdomen and black longitudinal bands on both sides. Its relationship with sharks is very friendly. Whenever sharks go on a hunting trip, they follow closely, as if they were like guards guarding cars, imitating its every move accurately. Sometimes, the guide fish will swim to the front to detect the situation, but they will soon return to their original position. Sharks never hurt friends and give them leftovers. It turns out that the guide fish is the "cleaner" of sharks. It often swims into the shark's mouth to help the shark clean up the debris between his teeth. With this relationship, sharks certainly won't eat guide fish.