Signs that can indicate a potential problem can be both physical and behavioural. Physical signs common to all types of animals can include uneven action, one-sidedness, tripping, difficulty bending and uneven muscling.
Behavioural signs in horses include stepping away or dipping the back during tacking up or mounting, resistance, grumpiness (biting or kicking) and rearing/bucking. In dogs you may notice yelping, a dislike of being touched, reluctance to perform certain tasks, reduced activity levels or the dog behaving generally out of character.