The original answer presents direct evidence that animals understand the concept of death. For example, it says that when elephants pass the remains of old friends during migration, they stop and appear to grieve. We cannot be certain what the elephants are thinking because we do not yet know how to communicate with them.
However, we can communicate with animals such as chimpanzees through sign language. In one case, a young chimpanzee died during surgery, and the trainer had to tell the chimpanzee’s mother in sign language that her child had died. According to the trainer, it was clear that the mother chimpanzee understood and reacted in the same way any human mother would.
More answers: Vegan Ethics FAQ.