"By immersing a live shellfish in water at cooking temperature you kill it and cook it in one operation. But ... to plunge a lobster or a crab, living, into boiling water is to torture it. Crabs shed claws (a sure sign of terror in the crab) and lobsters scrabble desperately up the side of the pot.
"This is the way to do it. Pour mildly tepid water - not cold or hot - over the live fish. This stuns it. Bring the water rapidly towards the boil, and the lobster will die before recovering consciousness - not a flicker of a whisker."