As a result, these pets often don't show obvious signs of illness until they are too sick to hide it anymore. (allpetsanimal.com)
By the time your pet starts showing other obvious signs of illness, for example lack of appetite, weight loss or low energy level, significant irreversible kidney damage has occurred. (healthypets.mercola.com)
This is a behavioral adaptation of a creature at the bottom of the food chain: a wild bunny showing obvious signs of illness becomes an easy target for a predator. (therabbithaven.org)