Crabs can’t be eaten the next day after a night’s death, because crabs belong to scavenging food, and they harbor many bacteria, microorganisms and parasites. After the death of crabs, these bacteria and microorganisms will reproduce in large quantities and secrete a large number of hazardous substances, which may lead to food poisoning, gastrointestinal infections, abdominal pain, diarrhea and other symptoms, and even systemic poisoning symptoms. Crab body also contains a large number of histidine, crab in the dying or after the death of the body of histidine will decompose to form histidine ammonia, and histidine ammonia belongs to the toxic substances, the longer the crab death time, the body of the histidine ammonia will accumulate more and more, and then the toxicity of the crab will be more and more, and even if the crab is boiled, the toxin in the crab body is not easy to be destroyed. In addition, when the crab is dying or after death, the crab decomposition and consumption of protein in the body will also form histamine, the protein content of the crab body is greatly reduced, and people in the consumption, the crab body of histamine will cause allergic reactions, mainly manifested as vomiting, diarrhea, local skin itching or edema.