Changes in behavior or temperament

• Aggression 

• Hiding

• Sitting still or haunching up

• Disinterest in people or other pets/reluctance to play

• Unusual vocalization

• Lethargy or restlessness

• Neglecting to groom themselves or overgrooming in a given area

• Loss of appetite

Limping or lameness

An abnormal gait

Difficulty climbing the stairs or jumping

Difficulty getting up after lying down

Stiffness 

Swelling or inflammation