blimp:
Well the clues are there. I have read it more than once. He is dead from when he shouts "Moth(er)," which is traditionally the last word drowning sailors utter before they perish beneath the waves. Also the cracks start to appear when he sees the lobster, which is pink!!
Agreed the clues are there, Blimp, but it's easy to think he's going mad and hallucinating, which is his own last-ditch interpretation. And I guess "Mother" is what a lot of people cry in extremis whether they then die or not. Actually I found the story so compelling, I read it first time at pace and didn't stop to consider what was really happening
I like "The Inheritors" just as much - a very credible picture of the last Neanderthals, though now scientifically outdated (Neanderthals almost certainly did have language).