It’s not easy to tell when a cat is in pain. They mask their discomfort well, but recent research suggest that facial expressions of cats can expose how they feel. Using ‘grimace scales’, scientists use the animals’ expression to try and interpret how they are feeling.
The grimace scale uses a series of images of expressions, showing how they change between feeling no pain and moving up the pain scale. The first grimace scales were created using mice, but scientists have now developed a range of grimace scales for other animals including horses, sheep, piglets and cats. Perhaps unsurprisingly, many animals show pain in their faces in the same way. Obvious signals to look out for include:
- Squinted eyes
- Flattened ears
- Drawn back ears
- Tense nose, mouth and cheeks
However, many animals have different facial musculature and with the diversity of breeds it can make cats appear very different from one another. These differences can make understanding pain expressions difficult. Another problem with cats is their solitary nature. Cats don’t want to appear weak to their competitors and so they are not likely to make it obvious when they are suffering.
One-way humans often conclude that something might be not quite right with their cats is through behaviour signals. For example, cats will often go and hide or go quiet. Often cats will show no signs and act as normal meaning their illness goes undetected for a long time. Therefore, researchers have paid attention to the cat and created an approach that will hopefully result in an automatic detection of facial expressions. Cat expressions were annotated using almost 1000 images showing the change of expressions as the muscles contract. Some images used were taken before and after surgery and a few key features that are linked to pain.
- Narrowing of the eyes and the eyes moving further apart
- Mouth and cheeks appearing smaller and more drawn in towards the nose and eyes
- Downward position nose closer to the mouth and away from the eyes with the nose positioned more to the left than the right
- Outer ear differences with the right ear appearing narrower than the left and further down the side of the face
This very subtle changes can easily go missed even by vets and other professionals. It can be especially difficult if the vets are unaware of what the cat usually looks like and their general everyday expression. There is potential for an app to be developed that will help determine the pain level in cats. When completed, such technology will make it a lot easier for cat owners to see the pain that cats are trying so hard to hide.
Read more about the geometric morphometrics for the study of facial expressions using cats, here: https://www.nature.com/articles/s41598-019-46330-5