CALGARY -- They may appear aloof or peaceful, but a scientific study says cats might be suffering in silence.

Dr. Daniel Pang from the University of Calgary's faculty of veterinary medicine says cats are notoriously hard to diagnose when it comes to their pain levels.

Pang and Dr. Paulo Steagall from the University of Montreal have developed a scale that looks at feline facial expressions, including ears, eyes and even whiskers.

Closing or narrowing eyes or flattening ears can be a sign that the animal is in pain.

Tense whiskers are also a clue.

Pang says the scale can be used by veterinarians and owners to figure out if a cat is hurting.

He says vets have historically underprescribed pain medication to cats as opposed to dogs.

He suggests that's because owners spend more time with their canines and can more easily assess when something is wrong.