Dealing with pain is very individual in humans and just as individual in canines. Dogs typically hide their pain; or at least they try very hard to hide their pain. Showing pain displays a weakness and in a pack, weakness within a pack is undesirable. Evolution has taught dogs to conceal their pain; even severe pain may only be barely visible and only to the dogs guardian. Often it is in the form of odd behavior that we realize that our dogs are in pain. Over all my years of living with dogs; all have been very different and that goes for how they display their pain as well.
Tilley has got to be by far my hardest read; she is a master at concealing pain. My male Clyde who lived with us before Luke was the worst; he was a screamer. He had no problem letting everyone know he was in pain and it was a prolonged agony he liked to portray. If you stepped on Clyde's foot he let out a blood curdling scream that went on for a solid minute or two, it was horrible. Tilley on the other hand will quietly pull her foot away and simply give you a brief eye contact.
In the wild; weakness can get you killed. You are a target for predators if for some reason you are physically handicapped and even within your own pack; the other members may cull you to protect themselves. So you don't let anyone know if you are in pain. With our own dogs; this can leave a canine guardian in the dark until the pain is so severe that the symptoms start to show. And at that point it can be past the point of return. This is one of the reasons that watching and knowing your dog and their behavior so well is highly important.
The signs can be so small; a tiny limp can result from a year long of hiding a sore leg. Less robust excitement about food, a walk or ride in the car can mean big trouble. Many dogs resort to aggression when dealing with pain which can be read as a sign that a dog is going bad. Any abrupt change, ever so slight; some form of behavior out of the ordinary for an individual dog can be a result of pain. This should always be addressed; it may not be the cause but it may be.
Dogs are truly masters of smoke and mirrors. It is up to us to see through it all.