Accurate assessment of animal pain is essential for welfare but has historically been limited by anthropocentrism and underestimation of non-human pain experience.
Pain undertreatment in non-human animals was historically justified by skepticism about animal sentience. The development of species-specific grimace scales representing facial pain expressions has revolutionized assessment in research and veterinary contexts. Recognition that animals actively conceal pain as a survival strategy means welfare-conscious care requires proactive pain management rather than waiting for behavioral signs.