My cat's tail bristles when he plays

Cats use their tails not only to walk, hunt, jump, etc. but also to express their moods.

Which muscle makes their tails bristle?

The muscle is called the hair erector muscle and is responsible for raising the hair on the tail when it receives a nervous stimulus. It is similar to humans when we get goose bumps.

When can their tails get bristly and why?

Our feline friends get their tails involuntarily bristled when playing due to an adrenaline rush caused by the release produced by the sensation of chasing their prey. Perhaps they are taking the game too seriously if, apart from bristling their tails, they turn sideways and get bigger. Maybe we should either stop the game, or change the toy for one that gives them more reassurance. Apart from playing, there are many other reasons why our cats may be getting their tails bristled:

-    Pain or illness, which would make it necessary for you to call your vet for an evaluation.

-    Low fever: when their temperature rises they can bristle their tail or body hair in combination with tremors.

-    Decrease in appetite: Your cat may be bristling with some of the health issues described above and you may also find that they have stopped eating, so seek advice from your vet as soon as possible.

 
-    If they are cold, their fur may bristle to maintain body heat, just as other mammals do by hollowing out their hair at low ambient temperatures, creating a layer of air between the hair and the skin, which acts as a thermal insulator.

-    When they feel that they are facing a threat which, true or not, causes them an adrenaline rush to put the body on alert. It is possible that, along with the bristling of the tail, we may see our feline friends walk sideways, grow bigger, growl, flatten their ears or have their pupils dilated. They usually get that way to scare their opponent, looking bigger than they are.

-    Out of fear or insecurity due to, for instance, a sudden noise that has frightened them. Once they feel that everything is fine, the bristle will go down again.

We should always pay attention to our little furry friend's body language so we can act accordingly. There are many cases of stress or aggression in cats that start because their keepers were unable to interpret when they should stop playing or petting them, which caused the cats to become a little more stressed day after day and end up assaulting them assiduously.

Alba Serrano, canine and feline psychologist and Master in Clinical Ethology from the UAB, @enlamentedelosanimales.