If your cat is clearly healthy as observed in a non-expert’s way, it is not abnormal or a sign of a health problem if their back ripples when gently touched. It is more likely to happen if your cat is unaware of what is going on. It simply means that your cat is slightly irritated by being touched on their back for whatever reason. And this is also linked to another form of feline behaviour which is instinctive.
Back ripple a general sign of displeasure
The ‘back ripple’ is a general sign of irritation of dissatisfaction. There is an overlap in these emotions. You’ll see it sometimes when a walks away from a bowl of food which displeased them for instance.
Under the skin of the back there is a large flat muscle called the cutaneous trunci. It twitches involuntarily in response to being touched on the skin resulting in this twitching action. I believe this is very similar to what we see with many animals who twitch their skin to remove flies on their bodies. It’s simply a form of removing a source of irritation.
Slight irritation or dissatisfaction
And looking at the video it is hard to deny that my assessment is correct. Look at the face of the cat at the end of the video and she looks a little bit irritated. She is resting calmly and then her owner comes up behind her and gently touches her back. She was unaware that this was about to happen and did not link the feeling with the person. It may have felt like an insect landing on her back.
It her owner had stroked her back it would not have rippled like this because she would have known it was her owner and that she was being petted i.e. stroked which is the equivalent of allogrooming (mutual grooming).
A cat will not ripple their back like this every time you touch it. It probably depends upon the mental state of the cat at the time. Cats are sentient animals. They have emotions. They might be in a particularly relaxed state of mind and are slightly irritated because of a disturbance on their back.
But if they are active and interacting with their owner their back muscles would not ripple in this way if you touched that area. This is because a touch from their owner is predicted and a known form of activity.
So, this is a perfectly healthy, normal reaction. It is the equivalent of a human brushing off an insect which has landed on their bare arm.
Dogs and other animals
Dogs might do the same thing and it will be a normal reaction with no health issues. It depends on whether there are ancillary symptoms. Straight back rippling when touched and nothing more in a healthy dog can only be a benign, instinctive reaction about which the owner should be unconcerned.
Feline hyperaesthesia syndrome
This disease is an entirely different kettle of fish. The interesting point about this question is that Google search results only point to a little understood and rather disturbing condition suffered by some cats called feline hyperaesthesia syndrome as the cause for the rippling that we see in the video.
This is simply untrue. A cat does not need to suffer from feline hyperaesthesia syndrome for their back muscles to ripple when it is touched in this gentle way as we see in the video. I am stressing the point.
The symptoms of feline hyperaesthesia syndrome include rippling or twitching of skin on the lower back for no apparent reason and, sometimes, after being touched. The syndrome also includes symptoms of: dilated pupils, jumping and running, excessive meowing and other noises. The cat might chase their tail or bite and lick their lower back and sides. They might experience pain or discomfort when petted or touch and they might be tired.
These symptoms are not presented by the cat in the video on this page. So, there is a difference here between a bona fide medical condition which is little understood and a simple reaction to being touched which is slightly irritating.
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