Squid can not only swim fast in the sea like fish, but also have a set of stunts to cast a "smoke screen". There is an ink sac in squid body, which contains ink glands that can secrete natural ink. In case of enemy injury or crisis, the ink sac contracts and shoots ink. In an instant, the sea was full of "black smoke" and it was dark. It took 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 is an expert in Qiang Bing. Its body is like a rubber bag with internal organs inside. 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 mouth that grows on the top of the head has a horny jaw and can bite food. Squid's feet are born on the top of the head, so they are also called cephalopods. Eight of the 10 feet on the top of the head are short, and the inside is densely covered with suckers, which is called the wrist; There are also two long feet that can move freely, called touching wrists, and only the inside of the front end has suction cups. Wrist and wrist touching are the hunting and fighting weapons of squid. Not only the weak life will be killed by the squid's wrist, but even the giant whale in the sea will be difficult to deal with when it meets the big squid with a length of more than ten meters. There is also a funnel on the ventral surface of squid head, which is not only an outlet for reproduction, excretion and ink discharge, but also an important exercise organ of squid. When the squid shrinks, the water in the bag-shaped body can be quickly ejected from the funnel mouth, and the squid moves forward quickly with the help of the reaction force of water, such as a strong crossbow leaving the string. Squid usually moves backwards because the funnel usually points forward. 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 shell of squid gradually degenerated and was completely buried in the skin, and its function changed from protection to support. The shell of squid is also called "cuttlebone" and can be used as medicine. Squid lives in the deep sea and swims from deep water to shallow sea 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 spawning.