According to the query of Doctor Youlai. com, the bacteria in the gastrointestinal tract will multiply after the death of the crab, which will lead to protein decomposition of the crab and easily lead to gastrointestinal infection. After the death of the crab, histidine in the body will decompose to form a toxic substance group ammonia. As time goes on, the more it accumulates, the more it can't be eliminated by steaming, so the crab can't be eaten after being refrigerated for one night.