Squid can not only swim fast in the sea like a fish, but also has a set of stunts to cast a "smoke screen". There is an ink sac in the squid body, which contains ink glands that can secrete natural ink. In case of enemy damage or crisis, the ink sac shrinks and shoots ink. In an instant, the sea water is full of "black smoke" and it is dark, so it takes the opportunity to escape. It can also use the toxins in ink to anesthetize small animals, so it is also called cuttlefish. In fact, squid is not a fish, but a descendant of mollusks. Among mollusks, squid can be called Qiang Bing's expert. Its body is like a rubber bag with its internal organs wrapped in it. There are fleshy fins on both sides of the body, which are used for swimming and keeping balance. The head is short and there are developed eyes on both sides. A long mouth on the top of the head, with horny jaws in the mouth, can bite food. Squid's feet are born on the top of the head, so they are also called cephalopods. Eight of the 1 feet on the top of the head are short, and the inner side is densely covered with suction cups, which are called wrists; There are also two long, free-moving feet, which are called wrist-touching, and only the inside of the front end has suction cups. Wrist and wrist-touching are the predation and combat weapons of squid. Not only the weak life will be killed by squid's wrist, but even the giant whale in the sea is difficult to deal with when it meets a big squid with a body of more than ten meters. There is also a funnel on the ventral surface of the squid head, which is not only an outlet for reproduction, excretion and ink, but also an important exercise organ of squid. When the squid shrinks, the water in the pocket-shaped body can be rapidly ejected from the funnel mouth, and the squid moves forward rapidly with the help of the reaction force of water, such as a strong crossbow leaving the string. Because the funnel usually points forward, the squid usually moves backwards. The special structure of squid body enables it to swim quickly. In order to adapt to this swimming style, in the long-term evolution process, the squid shells gradually degenerated and were completely buried in the skin, and their functions changed from protection to support. The shell of squid is also called "cuttlebone" and can be used as medicine. Squid lives in the deep ocean, and swims from deep water to shallow coastal areas to lay eggs in the warm spring breeding season every year. This phenomenon is called reproductive migration, and a large number of squid die offshore after laying eggs.