UPDATE: More Info On Dog Pain Diagnosis

An ailing pooch will exhibit behaviors that at first may seem unrelated to pain. They might chew up carpets, or their own fur, or become incessant barkers.

Some experts say animals will instinctively try to hide their suffering from outsiders. Typically, pets may cry to their masters for help when in pain, but they tend to act indifferently in front of a lab-coated stranger.

"When a dog shows abnormal behaviors or movements, it is possible it is in some kind of pain. We rely on the owners to keep a careful eye on their pets and look after them," Nishimura said.

Traditionally, veterinary medicine has shown little interest in animal pain, but things are changing. Now, doting owners want to do what they can to keep their aging pets comfortable and living as long as possible.