How do vets assess pain in animals?
By observing behaviour and posture, because animals cannot report pain and — crucially — many actively conceal it, which is an evolved response that makes assessment genuinely difficult.
Why concealment happens. A visibly injured prey animal is a target, so rabbits, guinea pigs, birds and reptiles hide pain and illness until it is severe. By the time a rabbit looks unwell it is frequently very unwell. Cats also mask pain strongly; dogs somewhat less so.
What clinicians actually look for:
Posture and movement — hunching, reluctance to jump or climb stairs, stiffness after rest, shifting weight, an arched back, a lowered head.
Facial expression. Validated grimace scales exist for several species, scoring features such as ear position, orbital tightening, whisker position and muzzle tension. These are a genuine advance and are used clinically.
Behaviour change — hiding, reduced grooming or over-grooming one area, irritability, altered sleep, reluctance to be touched, going off food.
Vocalisation, which is far less reliable than owners assume; many animals in significant pain are silent.
Response to analgesia, which is sometimes the clearest diagnostic — if behaviour normalises on pain relief, pain was present.
Why chronic pain is missed. Owners describe it as "slowing down with age". Osteoarthritis is extremely common in older dogs and cats and is substantially underdiagnosed, because the changes are gradual and interpreted as normal ageing. A cat that has stopped jumping onto the windowsill is telling you something.
What owners are best placed to notice, and what vets ask about: changes in routine, sleeping position, appetite, litter box use, willingness to be handled, and things the animal has stopped doing. Video at home is genuinely useful, since animals behave differently in a consulting room.
What has changed in veterinary practice: pain is now assessed routinely rather than assumed absent; multimodal pain relief is standard; and the historical belief that post-operative pain "keeps them quiet" is long discredited.
General information, not veterinary advice.