On the Internet, a standard acronym appears when a statesman dies: RIP. It means, rest in peace. RIP reveals that even in modern times we want to believe that after death there is something that needs ‘rest’ and ‘peace’. That death is not a full stop. This is an indicator of the absence of scientific thought, and a belief in the idea that something outlives the death of the body.
There is, as yet, no scientific proof that something survives death. All religious and occult views on soul, spirit, and ghost remain personal opinions. RIP is essentially an expression of subjective truth, not objective truth, an imagined reality or myth that many subscribe to, whether they are religious or secular.
Animals do not say RIP. They do not have the wherewithal to imagine such realities. Some animals mourn their loss, briefly, and move on. No one builds tombs and holds memorial days. Death for animals is a reality. For humans, it is a mystery. And we use elaborate stories to structure this mystery.
RIP has its roots in Christian and Islamic mythology, where after death, the spirit waits in purgatory till the end of the time: Judgment day (qayamat) in Islam, and Second Coming of Christ in Christianity. Then the faithful will rise to heaven. Until then, we hope the dead rest in peace. This concept of the afterlife can be traced to Greek mythology and before that Egyptian mythology. Chinese believed in the land of ancestors, to which the dead departed. In some cultures, dead kings and sages become gods and guardian spirits of the living. In some cases, the dead refuse to go into the afterlife and stay back as ghosts, troubling and tormenting the living. That is when you call ghost-busters.