HOW do cats purr?

This is NOT about why cats purr but how they do it. I'll say it again for Google, this article is about how cats purr. And I'll tell you right away that the scientists are slightly unsure even today how they do it. There have been several theories postulated over the years. 

One looks very outdated now which is based upon turbulent blood passing through a cat's veins and heart causing the sound of the purr. I think we can dismiss that categorically for obvious reasons. 

Another theory was called the "false vocal chord (cord) theory". This theory refers to the presence of a 2nd pair of chords thought to be the secret behind the extraordinary purring mechanism. That theory states that purring is no more than noisy breathing of the type that humans indulge in when they are asleep i.e. snoring.

I think we can dismiss that theory too. The modern theory is the one stated in the video below.

Note: This is a video from another website. Sometimes they are deleted at source which stops them working on this site. If that has happened, I apologise but I have no control over it.

This states that the laryngeal muscles are the source of the famous cat purr. These muscles are responsible for the opening and closing of the glottis, which is the space between the vocal cords. They separate the vocal cords. Studies have apparently shown that the movement of the laryngeal muscles signal from a unique neural oscillator in the cat's brain. 

Like I said it is all very mysterious and hard to visualise. I would love to see an animated film on it to allow me to better understand it. One important factor about the cat purr is that it takes place on the in breath and out breath i.e. on inhaling and exhaling which means that it is produced during the entire respiratory cycle. Vocalisations such as meowing occur on the exploration of the breath.

Kittens purr while suckling. They drink and vocalise the purr at the same time.

Image in public domain and created by MikeB.

There have been some studies (not many!) on how cats purr. One was 1st published in January 1991 titled How Cats Purr. It's published on the ZSL Let's Work for Wildlife website. It is highly complicated but they measured the purring in domestic cats, mountain lions and cheetahs. Some large cats can purr but the big cats can't. They can roar instead although the roar is a long-range call whereas the purr is obviously a short-range vocalisations.

The study states that the frequency of the domestic cat purr is 26·3 ±; 1·95 (S.D.) Hz. The frequency at mid-expiration exceeds that at mid-inspiration by 2.4+ or -1.3 Hz. Mid-expiration means the middle of the outgoing breath and mid-inspiration is the middle of the incoming breath. The frequency of a domestic cat's purr does not change with the age of the individual.

Cats can purr simultaneously with other vocalisations. They can also of course drink simultaneously with purring. The scientists used two-channel acoustic measurements and they confirmed that the "primary mechanism for sound and vibration production is a centrally driven laryngeal modulation of respiratory flow."

This supports the statement made above. They are saying that the laryngeal muscles alter the flow of airflow while breathing causing the purring sound.

On an associated subject, one study published June 28, 2020 titled Emotion Recognition in Cats states that domestic cats are able to recognise human emotions in detecting visual and auditory signals. In other words, they are recognising the sounds that humans make and their body language and movement in order to assess human emotions. That's what I glean from the summary. I would argue that they also employ their knowledge of the history of the relationship through rhythms, habits and routines.

Domestic cats are very much into the rhythms and routines of life in a human home. They understand and recognise the movements of the human companion and caretaker. When that changes, they can read something into it when combined with the human's voice i.e. vocalisations and their body language. That's my take on the conclusions to the study but I've added a little bit to it.

If you can add some info, it would be very welcome. I have written on this three times before!! Click this link for the last in that trio.

It's interesting but judging by the viewing statistics very few people want to know how cats purr. I put quite a lot of effort into this page but nobody is viewing it! I don't mind that much but it would be nice if they did. And while I'm adding an update, I will tell you why cats purr. It is not simply because they are content, although cats do purr when they are content, it is also delivered when they need friendship. You could say purring is a thank you for friendship given and a request for friendship needed. That's why you will see (correction: hear) domestic cats purring sometimes when they are frightened and in pain. It is said that the frequency of purring can heal which may explain why they sometimes purr when they are in pain.

Why do cats purr and knead? It is National Hug Your Cat Day!

I'm told that it is National Hug Your Cat Day 2021. When you hug your cat, he should purr. Purring and kneading go together with drinking milk for a newborn kitten. I guess that this is when it all starts. A newborn kitten goes to his mother's breast and kneads it to encourage the flow of colostrum which is so important to him. He has his own nipple with his name on it to avoid conflict! While he drinks, he also purrs in contentment. It is quite a feat to be able to do this but it is all easy and natural for a cat.

Human-cat interaction which is likely to elicit a purr from the cat and warm words and a smile from the person. Picture: Pixabay.

Purring

But purring does not always mean contentment. There is a multi-functional aspect to its existence. It obviously means contentment. We all know that. But why do domestic cats purr when they are in a veterinarian's consultation room about to be euthanised, which does happen sometimes? Under these circumstances it means that they want affection. They are looking for a condition under which they can purr because they are frightened. It's a kind of request. It may also be a way for the cat to feel better. It may also be a way to tell the world that they are not frightened. It's a bit like a person whistling when he's terrified. People tend to hide their fear and certainly that applies to cats.

You can see that we don't know exactly why cats purr except that they purr when they are content. But the reasons are far more subtle and nuanced than simply that.

Kneading

As to kneading, it is far simpler to explain this feline behaviour. They do it, as mentioned above, for the first time in their lives when they want to express that colostrum from their mother's breast. But then they do it all the time, depending upon the individual cat, with their human companion and caretaker. They jump on your lap and start to knead your dressing gown covering your legs. I hope the dressing gown is covering your legs because if not you might feel it. Or, you will see your domestic cat companion kneading the duvet cover or a wet towel which you just used to dry yourself with.

In each instance, the item that they are kneading smells of you. They are soaked in your scent, which kneading behaviour because your adult cat regards you as a surrogate mother and instinctively seeks the comfort of his mother's breast and the milk that she produces. It is a clear indication that the adult domestic cat is reduced to a kitten in terms of their mentality when they are with their human companion. And therefore, they behave like a kitten sometimes. And in doing this when they snuggle up to their human their memories of being nursed by their mother come to the fore and they re-enact those early days and weeks.

But sometimes, the adult female domestic cat behaves like a mother to us. When they bring in those dead or dying animals from the garden which they have so comprehensively and skilfully hunted, they want to teach you how to hunt. They drop the animal on the kitchen floor and then kill it with that bite to the nape of the neck. Or they may suffocate the larger bird with a bite to their throat. You observe and in observing you learn how they do it. At that moment you are their kitten.

You can see, therefore, that domestic cats are somewhat confused as to their status within the home. The human is dominant because they provide food and security. But in a multi-cat home there is no hierarchy. There might be a dominant individual cat who is more aggressive and in lieu of that the human is the dominant individual but it is a two layered social structure which is not a hierarchy.

Cat owners should never stop their cat kneading them. This may be difficult because it may be uncomfortable but if you do you are behaving like a very bad mother and you will confuse your cat. The mother would never do this because she is nursing her kittens. And therefore, the cat owner has to behave like a mother and be loving and supportive towards their kittens. This does not include pushing them away because it feels uncomfortable. The best way to deal with this, if your cat consistently kneads under certain circumstances, it to prepare for it and wear clothes which protect you. You will know when it is going to happen because cats are slaves to routines. They will respond to those circumstances in the same way each time so it is predictable.

Clouded leopard purring. Photo: MikeB.

Postscript: people ask whether the wild cat species purr. Some do and some don't. The lynx and the clouded leopard, for instance, purr but it is said that the big cats don't. They don't have the voice box to do it. The clouded leopard is a medium-sized wild cat species and when he or she purrs it is a hugely resonant and loud sound which is highly enjoyable to listen to.

Cat drooling while purring and asks to be petted

This barn cat is drooling while purring. He likes the attention so much that he asks for more by tapping the man on his face, which is completely understandable. Cats do drool sometimes when purring as they are contented but purring does not uniquely signal contentment.  It is a more complex signal or symptom.

Drooling often means mouth health problems, particularly stomatitis, an inflammation of the mouth. You'll see it in neglected domestic cats or feral cats. Drooling when content has its origin in the nursing kitten who is ready to receive milk from his/her mother's breast. Drooling is preparation for the moment. I guess it is the production of saliva to digest the expected meal. And sometimes cats drool when kneading their owner as it replicates the kitten-mother relationship when feeding. It is an example of adult cats being kept in a permanent state of kittenhood in human-to-cat relationship.

Barn cat taps man on face for more petting please. Screenshot from video on this page.

Poor oral health is one of the most common cat health problems per insurance claims. It is a particularly common problem as cat owners tend to ignore it. They can't see into their cat's mouth to check except fleetingly when their cat yawns. And wet food can exacerbate, it is believed, tartar on the gum line. Dry cat food does not really help clean teeth although I feed my cat Hills Oral Care which I believe does help somewhat and he likes it (too much actually). It is a large pellet so cats have to chew on them more. I believe that normal sized kibble pellets are too small as some cats swallow them whole. Dry cat food is addictive because it is sprayed with animal digest which is designed to taste great to a cat. The food itself is tasteless.

Try and check your cat's mouth for oral health. It is very important. Gingivitis precedes stomatitis. One sign is bad breath. This may help diagnose stomatitis.

Poor oral health is in the top 10 feline health problems.

Why Cats Purr When Under Duress

The classic reason why cats purr is because they are content.  That is the image we have but since the age of the Internet most of us now know that cats purr at other times, when for example they are in great pain, injured or even dying.  Contentment is not only the reason for purring.  Dr Morris says that this can be explained if we decide that purring is a signal indicating a need for friendship.  It is signal which says to an owner “thank you for your friendship given".

Some people still consider that purring is a mystery.  They believe that we still don't know why cats purr because it occurs on so many occasions other than when they are content.  I wonder if we can look to ourselves for an explanation.  Often when people are under duress or stress they present to the world an image that they are unconcerned.  They do this by trying to look calm and sometimes they vocalise in a way which indicates that they are calm and content.  Some people whistle when they are under stress or they might become more talkative.  Some people might hum as a way of looking calm and also calming themselves.  These are survival instincts which are still present in humans. I wonder whether these human behaviours shed some light on why cats purr when they are under duress?

My instincts tell me that cats purr when they are under duress as a way of calming themselves and presenting to the world that they are less concerned than they really are, as a means of survival.  That is my personal assessment and it is different to that of Dr Morris.

Cat Purring As a Request For Food Or Care

Although people think of the cat purr as a sign that the cat is content, it is employed in a wide range of situations.  The situation nearly always involves contact between the purring cat and either another cat or a person.

Photo by yellowcloud

Kittens purr from birth and do it while they are suckling a bit like a ventriloquist drinking liquid while projecting his voice to a dummy! The purpose is probably to encourage their mother to continue to nurse them.

Recently, investigations into the cat purr have indicated that the domestic cat can sometimes employ meow-like sounds within the purr.  Some scientists have stated that domestic cats who do this have learned to push the parenting button of the human by creating a sound that somewhat mimics the sound of a baby crying.

This modified purr has been described as a food-soliciting vocalisation.  The cat is asking for food, utilising the classic but modified purring sound.  This sound is hard for a person to ignore; hence the cat gets his food on request.

This manipulative sort of purring may also explain why cats purr sometimes when in pain or, for example, when in the veterinarian's consulting room at his clinic.  In this instance it is possible that the purr is not a request for food but a request for care and attention from the cat's "owner".

As the request is often followed by care and attention from the owner, the cat learns that it works which reinforces the behaviour.  This would be an informal form of cat training or the other way around, the cat training the person.

How cats purr

Article by Michael Broad

Are cats supposed to pant?

The answer is yes, under certain conditions. They are supposed to pant when hot and/or stressed or frightened.

Panting is a normal event after exercise for example. My lady cat pants when she travels in the car. She gets agitated and overheats a bit and starts to pant. This is only moderate but if a cat pants excessively and if it is labored watch out for heat stroke.

Panting lowers the cat's body temperature. Water in the mouth, on the tongue and in the lungs evaporates and cools the cat. The cooling effect comes from the process of the latent heat evaporation.

Why Do Cats Purr?

Here is the definitive answer to the question, "Why do cats purr?" The answer that is usually said to be the obvious one - that the purring cat is showing his or her contentment - is not true.

This is because cats in great pain, those who are injured, in labour and even dying or even sometimes at the vets being euthanised, purr loud and long (or it can last a second³). Kittens purr when they drink mother's milk purr and the mother purrs back. They also purr when being groomed by mother or by siblings. Kittens start purring when a few days old¹. All domestic cats purr. Sometimes cats purr when hungry. Body contact between the sender of the purr and the receiver may be an important factor in instigating it³.

Cats purr when contented also but it does not only happen when the cat is content. How do we find a reason for cat purring that encompasses all the circumstances under which it might happen?

Dr Desmond Morris in his famous book, Cat Watching, which is still probably the master work on cat behavior despite being first published in 1986, says the following.

"Purring signals a friendly social mood." It can act as a signal to ask ("the need") for friendship or say thank you for friendship received. Some cat behaviorists believe cat purring is a signal that the cat is not a threat². I prefer Dr. Desmond Morris's all encompassing explanation. Purring is classified by scientists as a "close-range felid vocalisation". It is used most commonly between mother and kitten³. This, then, is the answer to to, why do cats purr?

When purring is used by a kitten in the first days of his or her life it is a signal to the mother, when suckling, that the kitten is receiving milk. This reassures mother. Her return purr acknowledges the message and tells her kittens that all is well with her too. Kittens and mother usually purr continuously while nursing¹. Kittens aid the flow of milk by threading the abdomen (we know this as kneading, which frequently happens if our cat is on our lap). Cats often purr at the same time.

Calico cat - Photo by Crane1989

Purring can take place while the cat is drinking, therefore. It is a two way action - the sound being produced on inhaling and exhaling.

The big wildcats cannot purr. They make a sound similar to the purr but it is a one way (exhalation) process. The four big cats can, however, roar (see tiger roar). The cheetah is not classified as a big cat and it can purr². Its purr is much louder than the domestic cat but is it as loud as Smokey's purr (see below)? The Eurasian lynx also purrs. It is a vocalisation used by mothers nursing their kittens³.

Purring is classified as a "murmur pattern"¹. This is a sound that is produced with the mouth closed. The trill/chirrup is also made with the mouth closed.

Purring is produced in the cat's throat. It is not absolutely clear how it is produced. It is thought to be produced "through (the) alternating activation"¹ of the muscles of the larynx and diaphragm. There is a build up of and release of air in the glottis. When we feel the purr by placing our hand gently against the neck we feel the vibrations of the air and muscles. The sound is louder and rougher when produced on breathing in.

Cats purr in the "frequency range of 25 to 150 Hz². This is a low amplitude murmuring sound³. An interesting theory is that cats might be instinctively trying to heal themselves at the "cellular level". This is because at the frequency range of the purr, sound is thought to be "beneficial to healing"².

It is said that a cat's purr is unique to the individual cat². It can usually be heard three meters away. However, one famous cat named "Smokey", who is described as a 12 year old British Shorthair (this means a random bred cat with short hair) has a purr that is so loud it is more noisy than a vacuum cleaner! His owner describes the sound as if "Smokey had a dove caught in her throat". She has had eight different homes. Are the two connected? I think so. The purr has been recorded at 73 decibels (dB). Guinness World Records are considering making it a record but there are no competitors. It would be a new classification.

Read about cat behavior.

Read about cat sounds.

Notes:

1. The Cat: Its Behavior, Nutrition and Health

2. Cat Owner's Home Veterinary Handbook - page 296 - 297.

3. Wild Cats of the World - pages 10, 422.



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