Celestia's scholar friend turned out to be a full-blooded cait sith (pronounced like "kate she"), also known as a "fairy cat."
Now, there is a widespread confusion, in regard to cait sith. In folklore, it is sometimes said that witches use them as demonic familiars. This is not entirely true, but it is not as far removed from the truth as other legends, regarding their association with witches: they do have the effect of magnifying the powers of witches like a focusing lens. Another story, regarding cait sith, is that they are halfway immortal, and they are said to have "nine lives." This also is inspired by truth but not altogether true: they actually live to full human life-expectancies, but there is a myth that they are getting reborn several times, which is just not true. There is a belief-system that states that cait sith are spirits of the land that take a physical form in order to attempt to communicate with mortals, being a sort of "land wight" or "genius of loci," which is used to explain why giving a cait sith a saucer of milk helps the cows produce better milk. Actually, cait sith are just incredibly proficient ratters, and keeping pests under control tends to lead to cows, who are deeply bothered by pests, being less stressed-out and in better temper, thereby resulting in better milk production: such mundane explanations don't seem to fit magical creatures, though, so it lacks appeal.
In fact, cait sith appear to be ordinary cats, but they are really a type of fairy. They tend to associate with witches merely because, culturally, human witches and fairy cats are both sorts of outcasts among their own kinds, yet they have the common trait of truly being peaceful, in spite of fearsome reputations. Cait sith are reputed, among other fairies, to be ferocious monsters that like to eat other fairies for breakfast. Cait sith really just prefer common mice. Witches are often regarded as being secretive about their arts, but the truth is that, if you give a witch the slightest indication that you are interested, then he or she will almost always end up telling you more than you wanted to know. Witches and cait sith have the common trait, then, of being amiable and generally peaceful outcasts among their own races, which makes them drawn to each other by that commonality.
However, cait sith also enjoy the company of lonesome college professors that drink too much coffee. The reason why is that cait sith are also inveterate bookworms and scholars, although they tend to prefer being ghostwriters and allowing credible human scholars to sign off on their work. Like most fairies that ever lived, cait sith get very annoyed when common people find out that they exist. However, scholars that mysteriously find themselves in the possession of large storehouses of receipts, estate records, or other documented evidence for their data, without any clear explanation for how they might have come by it, almost invariably have a cait sith working for them. Most people, however, assume that these cats are just pets they obtain in order to ward off feelings of loneliness.
However, because Celestia was a very good student, she was quickly able to spy a writing style and a method of research that did not line up with other publications by the same putative author, which had led to her writing several polite letters complimenting the scholar's work and also inquiring about the reasons behind this discrepancy. She had quickly found out that the scholar that had been signing off on certain publications had a pet cat, and she had then proceeded to verify that the cat was really a cait sith that had had a longtime fascination with economic theory. This one's actual name would have been difficult for a human to pronounce, so he just went by the name of "Bubbles."
"You humans are an endless source of fascination for me," Bubbles said as he walked along a level of bookshelves. Anytime he got to the end of one column of shelving, it looked like he ought to stopped by the side of the shelf, but the cait sith just nimbly wove his body around the obstruction and on to the next column, thereby easily moving about in the library along an apparently familiar route.
Oliver, who would have made a bright scholar if he had come from a more enlightened background but was, by no fault of his own, incredibly ignorant, had a nonplussed look on his baleful, green face. "But...why would a fairy of any kind, much less a cait sith, have any interest in human affairs at all?" he asked.
Bubbles looked wryly over his shoulder as he stood with his back arched humorously and his tail flicking against the spines of some books. "Are there not plenty of humans that objectify fairies as subjects of intense interest?"
"Yeah," Oliver admitted. "It is very strange to me, though. I mean...wouldn't fairies be better suited to studying...fairies?"
"No," Bubbles said firmly.
"Why?"
"Because our perceptions are colored by the prejudices of our internal politics. Different groups of fairies have truly ignorant stereotypes about one another, and our perceptions tend to be skewed in favor of viewing our own particular groupings as being more diverse and more influential than other groupings of fairies, alternately demonizing them or infantalizing them. Human research on fairies really ends up being much more accurate and detailed than the politically biased works we produce ourselves."
"Oh," Oliver said wondrously, "so it's like how people from different parts of certain countries have always seen themselves as 'gently shepherding' people from other parts of those countries to a united destiny, yet their accounts are always chauvinistic and skewed toward their own biases. An external view, while not always superior, can help circumvent those biases."
"Precisely!" said the cait sith as he bounded over to a desk where a book lay open, "and my own subject of interest is your economic system, this being only one volume among a vast collection that I have been amassing, in regard to the materials and services that are used by members of every possible occupation at every possible level. I have extensive tabulated appendices that detail historical fluctuations in prices. However, there is a reason why I ghostwrite all of my work and have it published under the name of an entirely different author."
"Why is that?" asked Oliver.
The cait sith wrapped his tail around himself smugly, and he smiled the opossum-smile of the cat that just ate the canary. "Anonymity," he said blithely, and he explained, "Merchants and craftsmen don't quietly let go of their trade secrets and don't tell just anyone the details of their processes or the true costs of their materials." Bubbles humorously put on the expression and posture of a perfectly innocent cat, though, and his point was apparent: "but I ask you, who takes notice of a nameless, little cat?"