York tries to appeal to Mrs. W by insisting that the horses might behave unsafely if they’re suddenly constricted by the bearing rein. So the fact that neither he nor Mrs. W seem to care about this suggests that they don’t much value safety, and they don’t see the horses as individuals who are going to have to get used to a more restrictive way of moving. And Black Beauty’s first-person narration shows readers exactly how terrible being restricted like this is. It hurts him, and Ginger’s temper is worsening. Ginger’s warning also suggests that if her owners aren’t going to be kind and understanding of what she’s going through, she sees no reason to play along. Put another way, they’re losing her loyalty.