Fragments are servants of the Glass Cat. They hunt down those their master marks, though it usually prefers to hunt for itself, much like the Black Dog's relationship with its Prowlers.
Fragments become less recognizably human as they progress over weeks or months. The longer a person is a Fragment, the more dry and cracked their skin, the sharper and harder their canines and fingernails, and the easier it is to see the organs beneath their skin as it grows translucent.
A sufficiently new Fragment, however, is indistinguishable from anyone else.