2, look at the weight: weight reduction, empty also means a long death time.
3, look at the legs: crab legs droop, very loose also means that the death time is longer.
Crabs must not be eaten when they are dead. When the crab is dying or dying, the oxygen acid in the crab will decompose to produce histamine. Histamine is a toxic substance. With the extension of death time, more and more histamine is accumulated in crabs, and more and more toxic gases are produced. Even if the crab is cooked, this toxin is not easy to be destroyed. Excessive ammonia nitrogen must be excreted from the kidneys, so eating dead hairy crabs is very bad for the kidneys.
People who eat dead crabs may have vomiting, abdominal pain, diarrhea and other symptoms. Even the half-dead "legged crab" is not suitable for eating. The infection rate and degree of metacercaria of Paragonimus larvae in live crabs are very high. Paragonimus parasitizes in the lungs, which can stimulate or destroy lung tissue, cause cough and even hemoptysis. If it invades the brain, it will lead to paralysis.