I looked out at the shadow pursuing him.
"...a cat?"
No, there was no way it was something so mundane.
Ah, it was just something borrowing the 'frame' of a cat. Even for a Mystery, some sort
of shape that at least approximated something real was necessary for it to be
actualized. No matter if it was born from magecraft, the interference that would have to
be dealt with if it took a completely unrelated shape would be considerable, if I was
remembering my lectures correctly.
"Ihihihihi! What even is that?! Is that really something made by modern magecraft?!"
As if he just couldn't hold it in, Add broke out into laughter. Conveniently, that was just
as Add was needed.

The Case Files of Lord El-Melloi II, Volume 3, Chapter 2, Part 3