Some signs are more clear than others that our pets are in pain.
Crying out, whimpering, flinching, and guarding areas of their body are generally well-recognized as signs of pain or discomfort. However, in their instinctive efforts to conceal signs of vulnerability (in the wild this is a defense mechanism), pets are very good at hiding signs of discomfort. Most times they will show much more subtle clues that there is a problem. Since we can't ask our patients what hurts (rather, they never answer us), we have learned to pick up on these subtle clues and recognize them as a symptom of pain.
Pet owners often tell us that their pet is limping, 'But he hasn't cried out at all.' What many don't realize is that limping is a sign of pain. Consider a person that is limping; they don't bear weight because it is painful to do so. Many times pets do not cry out, even if they bear weight on a sore limb. Joint pain and back pain often manifest as trembling, irritability, stiffness, hesitance to climb stairs or jump onto/off furniture, into/out of vehicles, etc.
This is a tricky one because many times pets conceal mouth pain very well, and often will give no indication that anything is wrong. Many times during annual check-ups we will discover abscessed teeth, fractured teeth, gingival masses/inflammation, and tooth resorption. We know from humans with these conditions that they are painful. But most times the pet has continued to eat perfectly normally, giving owners no strong indication of a problem. Subtle signs of mouth pain include drooling, dropping food out of the mouth, shyness to be touched around the head/face, less interest in chewing on firm/hard toys and treats, and preference for soft food over dry.
Redness or swelling of the eye is a pretty obvious sign of discomfort. But pets will also scratch or paw at their eyes, have discharge, and squint their eyes when painful.
Pets often scratch their ears, shake their head, or rub their ears on the floor, couch, etc. when painful. Most do not cry out even when their ears are touched, although sometimes they do if the pain is severe enough. They may even groan and lean in when getting an ear rub, or be very guarded about someone touching their ears.
Vomiting and loose stool/diarrhea are obvious signs of an upset tummy. Less obvious signs include tension when touching the abdomen, decreased appetite, bloated appearance, rumbling noises, lethargy, hesitance to walk/stand, and sometimes abnormal posture (arched back, excessive stretching in 'downward dog' yoga pose). Drooling or lip-smacking can mean tummy upset/nausea, even if no vomiting occurs. Many pets may appear to strain when having a bowel movement, and this is often identified by owners as constipation. Certainly, constipation can involve straining, but so can diarrhea and difficulty with urination.
Straining to urinate and bloody urine are easily identified by owners as a problem with urination. But urinary pain/problems often manifest more subtly before straining or passing of blood occurs. Inappropriate elimination (urinating or defecating outside the litter box with cats, or in inappropriate areas/inside the house for dogs), increased water consumption and amount of urination, increased frequency of urination, dribbling urine, and straining is all signs that can be associated with urinary pain/disease such as a urinary tract infection, inflammation within the bladder, kidney disease, prostate disease, bladder stones, etc. There can also be no signs at all. Cats may pluck/overgroom the hair on their tummies or become less social. Occasionally pets may cry out when urinating, but many do not.
General Subtle Signs of Pain
Subtle signs such as decreased energy level, decreased appetite, trembling, irritability, behavior changes, less socialization/hiding behaviors, and others can indicate pain from multiple sources. If you notice changes in your pet, it's important to contact your veterinarian to discuss your concerns. There may be underlying causes that aren't immediately evident that would prompt us to do a thorough physical examination and possibly diagnostic testing or imaging.
You know your pet better than anyone, so staying in tune with them and then filling us in on anything abnormal is the best way that we can work together to keep your pet as healthy and happy as possible.