Considering the number of mice my cat has killed, I tend to disagree that they have no concept of death at all. The extent to which they "understand" it is open to debate for sure. But whenever my cat catches one, he deliberately leaves it alive for a while to play with until he gets bored, at which point he promptly cracks its skull between his teeth to finish it off and tries to eat it(I usually stop it if I can so he doesn't get parasites). There's certainly some concept there. Probably not the same concept we have, but it's there in some form.