Your loud neighs shatter the quiet of the library, and elicit a responding cry of "What the fuck?!" Thumping, running feet in what must be heavy shoe race towards you. You cannot turn around here between the shelves, so it is lucky that the investigator appears in front of you, just past the book. She is a pretty girl, you realize, and young. High school, with the look of a track athlete, but with big bottlecap glasses that give her an owlish aspect. Your mind is racing, still just as intelligent as ever, and you stare at her as she re-iterates, "What the fuck?"
You whinny at her, desperately and your hooves clatter on the ground, your rump scattering a few books behind you. She looks you over, giving you time to examine her more closely. Freckled, a single long blonde braid, brilliant blue eyes, and lanky. Flat-chested, although she covers herself now by clutching a book of her own to her chest. A book, you think. No, The Book, you realize.
You're not sure when she snatched it up but that thing changed you, you need it, and you lunge out for it, teeth reaching clumsily to grasp it. She shrieks and stumbles backward, falling on her ass. By some dreadful trick or divine accident the book falls before her, opening as it does, and her hand thuds down on the middle of a large inky hoofprint. Your whiney of despair is echoed by her scream as she staggers to her feet, teetering on top of legs that are twisting beneath her and disobeying her commands. Her are shredding as she drops to all fours, forehooves forming as she falls, fingers fusing in time to clatter on the floor.
You can only watch stunned as your own recent change is mirrored by this girl's transformation. Her torso, thin and lissome, expands and swells, covering in light chestnut hair. It causes the thin blouse she wears to rip away, shreds of her bra falling to the ground, exposing vanishing breasts that slide down her torso towards her hindquarters. Her rump is expanding and her body growing and growing, human face stretching out as her scream becomes a loud neigh and a shocking corn-silk tail flickers behind her as the newly minted mare rises to her hooves. She's smaller than you by a good bit, some breed made for sprinting and dancing.
You can smell her, a rich smell unlike any you've ever experienced before and you can see by her flaring nostrils that her experience is not dissimilar at this moment. You stare at her where she stands in the wider avenue between shelves and you make up your mind what to do next...