It is best not to eat it. Crabs are a kind of scavengers with strong immunity, eat a lot of bacterial viruses, but they are suppressed by the crab's immunity, once the crab is dead, or even not dead yet, just dying, the bacterial viruses will multiply and breed some biotoxins. All you just need to see the crab half dead and spiritless, it is better not to eat it.

Dead can't be eaten, because the protein is converted to toxic protein after the crab is dead

Crabs can't be eaten when they are dead. Crabs are often caught trying to break free causing an increase in lactic acid in the body, which can lead to the rapid multiplication of bacteria in the body of the dead crab and spread to the crab meat. Bacteria will decompose the amino acids in the crab body, and then produce a harmful substance "histamine", causing allergic food poisoning; another possible substance is "histamine-like", which can cause vomiting, abdominal pain, diarrhea, so be careful when selecting.