So, do you begin cooking with a live lobster or a dead one? Certainly it should still be alive within a matter of minutes prior to cooking unless it has been previously frozen. While plunging the live lobster into the pot will surely be fatal, the thrashing tail is likely to cause burns from the boiling water or at the least, a mess.
From a scientific standpoint, the muscles toughen with the shock of hitting the boiling water, which means more chewing for the diner. If you go for the plunge method, put the lobster in head-first which should kill it pretty much instantly.
Some cooks are concerned about humanity issues of cooking a live lobster. In fact, research indicates the lobster has no central nervous system or cerebral cortex to register stimuli, thus the creature mostly likely can feel no pain. However, killing the lobster just before cooking is the preferred method.
There are several ways to accomplish this. Putting the lobster in the freezer an hour before cooking will do the trick. Quicker yet is to plunge the tip of a sharp knife straight down right behind the lobster’s eyes.
"Some cooks’ practice is to drive a sharp heavy knife point-first into a spot just above the midpoint between the lobster’s eyestalks (more or less where the Third Eye is in human foreheads). This is alleged either to kill the lobster instantly or to render it insensate—and is said at least to eliminate the cowardice involved in throwing a creature into boiling water and then fleeing the room. As far as I can tell from talking to proponents of the knife-in-the-head method, the idea is that it’s more violent but ultimately more merciful, plus that a willingness to exert personal agency and accept responsibility for stabbing the lobster’s head honors the lobster somehow and entitles one to eat it. (There’s often a vague sort of Native American spirituality-of-the-hunt flavor to pro-knife arguments.) But the problem with the knife method is basic biology: Lobsters’ nervous systems operate off not one but several ganglia, a.k.a. nerve bundles, which are sort of wired in series and distributed all along the lobster’s underside, from stem to stern. And disabling only the frontal ganglion does not normally result in quick death or unconsciousness."
For those who do not wish to wrestle with a thrashing lobster prior to cutting the spinal cord, place the lobster in a large pot in the sink. Begin filling with cold tap water and gradually increase the heat factor of the tap water until it is hot. This will desensitize the creature so you can cut the cord and put it into the pot or cut it in half for further cooking.