The other day I heard this chef talking on the radio about dropping lobsters into boiling water. The question was whether this or any other method of cooking live lobster was humane. Specifically he was focusing on the question of whether the lobster feels pain. The chef’s preferred method was to first put the lobster in the freezer until it stops moving and then drop it into boiling water.
Of course there is no way to know whether the lobster feels pain from being boiled alive but we can ask whether there is any theoretical reason it would feel pain. In creatures that feel it, pain is a selected response to a condition in the environment that is to be avoided. Notice an implication of this: being a (life-)threatening is a necessary but not sufficient condition for some environmental feature to induce the response of pain.
Apparently humans do not feel pain, or anything at all, when exposed to life-threatening carbon monoxide. Presumably that is because relative to the span of time it takes to evolve a protective painful response, carbon monoxide has not been a relevant threat for very long. No response has been selected for yet.
Does a lobster ever encounter hot water in its natural environment? Is there any channel through which natural selection would have given lobsters a painful response to being boiled? What about being frozen?