An article at Vice "Do Animals Understand What it Means to Die" is an interesting, if somewhat saddening, read. It also introduced me to the term "comparative thanatology", and contained this somewhat startling section:
If we are interested in animals’ relationship to death as a topic on its own, and not only in relation to humans, we have to also look way beyond practices that we can identify with. One example is when pets feed on their owners after they die. “This is an extremely common phenomenon, much more common than we want it to be,” Monsó said. Even with dogs, who have strong bonds with their owners, “we’ve seen examples of dogs eating their owners 45 minutes after the owner died and with food in their bowl.”
Monsó said the pattern of eating is also different than when a dog would be scavenging; when dogs scavenge, they usually eat the abdomen area first, but in these cases dogs focus on the face. “It’s a very disturbing behavior, but I think it's a super interesting one,” Monsó said. “But it's only discussed in forensic science papers. I think one of the reasons may be why it hasn't been deemed relevant until now has to do with the fact that it's not a behavior that we can really relate to.”
And here's a key section about what animal awareness (or lack of it) means for ethics:
Ben Bradley, a philosopher at Syracuse University, said there have been some philosophers who argue that the concept of death is necessary in order for death to be bad for you. As long as an animal’s life is painless, killing them is no harm since they don’t know what death means.
“If you can’t conceptualize something, then you can’t care about it, and so it can’t be bad for you,” he explained. “If this is right, then if animals don’t have a concept of death, their deaths aren’t bad for them. This would have important implications for how we treat animals, because it would imply that it is morally permissible to kill them for food, unless it were wrong for some reason other than being bad for the animals.”
Bradley thinks we should reject the claim that nothing can be bad for you unless you care about it. He wrote a book chapter on this called “Death Is Bad for a Cow,” and also a song of the same name, with the lyrics:
Listen to me and I will tell you how
When you take that cow to the butcher's knife
You deprive the cow of the goods the goods of her future life
Don't need to have a sense of self over time
Or know what it means to reach the end of the line
Death is a serious harm
Even if, even if you live on a farm.
Gonçalves said we shouldn’t wait until the concept of death is proven to try to treat animals in ethical ways. “We should prevent the infliction of unnecessary pain and suffering regardless of them having a concept of death or not,” Gonçalves said.