Animals on the seabed are characterized by their own activities. The sea cucumber crawls by muscle stretching and can only advance four meters per hour. The barracuda can swim several thousand meters per hour, and when attacking other animals, it is faster than an ordinary train. Squid and octopus can suddenly spray water in front of them and use the counter-thrust of the water to move back quickly. Some shellfish don't move on their own, but can ba underneath a ship for a free long trip. There are also some deep-water fish, they have their own light-emitting organs, swimming like twinkling stars.