Shadowsight  stared  at  the  impostor,  blood  roaring  in  his  ears.  He  no longer saw Squirrelflight. He forgot about Mothwing. He held his breath as Bramblestar’s  body  seemed  to  change.  Not  its  color  or  its  shape,  but  its posture shifted, its hindquarters hunching down and leaning to one side, the shoulders sharpening so that they seemed to strain at the skin and fur that covered them, the head lowering, the muzzle questing forward like a snake’s. Before Shadowsight’s eyes, Bramblestar seemed, despite the tabby pelt and amber gaze, to become another cat.

Darkness Within, Chapter 2