On Other Creatures
In Star Swirl the Bearded's time, tensions between the various species in our world were too high to allow his research to extend beyond the pony population. Even today, these tensions remain and make the examination of other species a very difficult process. Due to this we were unable to carry out anything more than preliminary investigations, and the results of these are summarized here.
The fundamental beginning to our observations was determining whether other creatures also have a magical essence related to their life. Use of the modified magic-detection spell (that which allowed perception of magical entities in an area) indicated that all animals indeed appeared to have some magic within them that left the body but persisted for a time after death. We could not delve further into the subject, but it seemed reasonable to assume that this essence was the same soul as in ponies; though we lacked evidence for this conclusion, it only appeared probable that this was true.
In addition, the phenomena of a soul fusing with another was not necessarily restricted to within a species. On one occasion in our investigation of pony souls after death, a researcher observed a pony soul fragment fusing into a griffon with whom the soul had been close friends in life. The griffon experienced the same change in personality and improved memory of the friend as that which occurred among pony soul fusions. Therefore, there were no physical barriers preventing souls from fusing with one another: it appeared in fact that the soul of one creature was of the same essence as the soul of another. This was only to be expected considering that there was only one magic that all magical essence was built of.
This was the boundary of our understanding of life and death in other creatures. Unfortunately we could not perform any soul tracking observations an any non-ponies due to the difficulty of finding any volunteers. We could only suppose that the phenomena life and death in other creatures was much the same as in ponies.
Conclusion
So ends this treatise on the natural phenomenon of death. What has been stated above constitutes the entirety of our present knowledge on the subject. Though there is certainly much more to be discovered, after twelve years of difficult research we and Princess Luna all felt that we had understood what we set out to determine. Thus our project came to an end, and I was set to the task of compiling our results into this document.
To the reader, I express my hope that this information will prove useful. I also urge them not to dwell too much on the thought of their death; a pony's life is too short, and eternity too long for any good to come of such an effort. There is one life lesson to be learned from all this, however: death will be easy, and life will have been well spent, if we leave our bodies as good people surrounded by friends.