Leech is about 5 cm long, gray-black-green, with suction cups at both ends. There are 6 gray-green longitudinal stripes on the back and a broad white belt in the center; The abdomen is dark gray. It really swims in waves by stretching muscles in the water, and advances by stretching suction cups and bodies on objects in the water. The saliva secreted by leeches contains hirudin, which can inhibit the activity of thrombin and prevent blood coagulation. When leeches suck blood and secrete saliva, the blood will continue to flow out slowly without coagulation. Bleeding with leeches will not harm the skin, the wound will no longer be congested, and the regenerated blood vessels will grow well and form a new blood circulation. Leeches cling to human skin because when the sucker touches the skin, it will form a vacuum state. But if you are bitten by a leech, don't pull it by hand, because it will suck harder when it encounters a sudden attack, so the more it pulls, the more it sucks. At this time, as long as you gently pat the sucked skin a few times, the vacuum state under the suction cup will be destroyed as soon as the skin contracts, and the leech will naturally fall.