Crows are called crows, and folks also call them "black old women". It belongs to the Ravidae with magpie, and it is indeed a beneficial bird. But people prefer magpie, but they are very disgusted with it. The reason is not only that they like to eat carrion, but also that crowing is considered as a bad omen. In the old days, when people heard crows, they thought something would happen. If you hear crows in the morning, you think it will be unlucky all day. If crows bark around the house, they think they are going to die. Therefore, there is a saying among the people that "crows mourn". When people hear crows crowing, they will scold them or drive them away with stones and clods. Of course, the saying that "the crow sends his funeral" is a superstition. But in real life, in addition to coincidences, some people have indeed seen crows hovering back and forth on the roof before the patient died, screaming. This is because crow is a bird with a mixed diet. In addition to eating grains, wild fruits and insects, there is also a prominent feature, that is, I like to eat rotten materials decomposed from animal carcasses. Long-term living habits, so that they have developed a particularly sensitive sense of smell, in a long distance, it is convenient to smell the faint smell emitted during the decomposition of corpses. Modern medical research has proved that before dying of a long illness, due to serious obstacles in the metabolic process, some cell tissues have begun to degenerate and decompose. At this time, the human body will release some faint smells, which will lead to the arrival of crows. This is the mystery of the "crow mourning".