Cancers are usually cooked alive: it is believed that they do not feel pain. In fact, such doubts exist not only around crustaceans, but in general all invertebrates: they simply do not have areas of the brain that respond to pain in higher animals.
On the coast of Ireland, 40 specimens of small oceanic crabs Carcinus maenas were collected. The animals were placed in separate aquariums, after which half of them were pulsed with a pulse length of 200 ms for 2 minutes at a frequency of 10 s. The second group of crabs was luckier: they played the role of control and were spared electricity.
Soon, the fact that they feel the pain became obvious. 16 of the 20 crabs of the experimental group began to actively move in their aquariums, and four tried to escape. Among the animals of the control group, no one climbed the walls, although 14 crabs also moved. However, in hemolymph - the "blood" of all stimulated crabs - there was a sharp jump in the content of lactic acid, the level of which tripled. It seems, they "meet the criteria of a painful animal". So, to their close relatives, crayfish is probably very painful when they are brewed alive.