“That one in there—he just sits and hisses.” The school caretaker pointed to a hole underneath the old building. I crouched down, peered in, and said, “Hello there,” to the dirty, scrawny little cat, who promptly hissed at me with all his tiny might. Hissing Sid, as he became affectionately known, was one of a colony of feral cats that my colleagues and I went on to rescue from the grounds of the school, where they were becoming something of a nuisance. After a little sojourn in a rescue shelter where they were all neutered and their kittens found new homes, the cats were relocated to a farm. Over the next few years, feeding them in their special cat shed on the farm every day, these cats became part of my life. Here, as they learned to trust me, they worked out new ways to communicate with me. Ways that included less hissing and more of the friendly sounds we associate with our sweet‐talking pet cats.

In a cat’s world, where smells are paramount, it must be a bewildering experience when they first hear a person speak. So many different, unfamiliar sounds directed either at another person or, even more perplexingly, at the cat. Humans are very preoccupied with the spoken word, babbling away at everyone and everything we meet. Intrigued as to what their “spoken” sounds mean, we have developed something of a fascination with the vocalizations of cats too. Nestled deep in the history books, a diary entry by the Abbé Galiani of Naples, dated March 21, 1772, offers some of the earliest recorded insights into cat vocalizations.

“I am rearing two cats and studying their habits—a completely new field of scientific observation . . . Mine are a male and a female; I have isolated them from other cats in the neighborhood, and have been watching them closely. Would you believe it— during the months of their amours they haven’t miaowed once: thus one learns that miaowing isn’t their love language, but rather a signal to the absent.”

Little did he know it, but Galiani was ahead of the game with his observation that his two cats never meowed to each other. The true purpose of meowing would only be discovered centuries later, when larger scientific studies of cats became more accepted.

Through the intervening years, feline literature embarked on something of a magical mystery tour of the apparent linguistic talents of cats. Writers mostly attempted to define cat vocalizations along the lines of human language, identifying consonants and vowel patterns and certain “human” letters in their cats’ speech. Reflecting on the differences between cats and dogs, Dupont de Nemours, an eighteenth‐century naturalist, wrote, “The cat, also, has the advantage of a language which has the same vowels as pronounced by the dog, and with six consonants in addition, m, n, g, h, v, and f.”

Some authors took this a step further to describe cats’ use of actual human words. In 1895 Marvin R. Clark, a musician and lover of cats, published an enchanting and slightly bewildering book titled Pussy and Her Language. In this he includes “A Paper on the Wonderful Discovery of the Cat Language,” apparently penned by a French professor named Alphonse Leon Grimaldi. In it, Grimaldi claimed to have elucidated the language of cats, providing an in‐depth analysis of the cat’s use of vowels, consonants (apparently used “daintily” by cats), and grammar, as well as words and numbers.

Grimaldi’s paper included a list of what he considered to be seventeen of the most important words in the feline language:

He went on to elaborate, “In the feline language the rule is to place the noun or the verb first in the sentence, thus preparing the mind of the hearer for what is to follow.” As if this weren’t skilled enough, Grimaldi also considered cats capable of counting. He compiled a comprehensive list, including “Aim” for number one and “Zule” for millions.

Grimaldi’s “translations” were not surprisingly met with mixed reactions; many authors dismissed them as nonsense. However, among his rather bizarre suggestions, he did include a few wonderful nuggets of insight. His description of an enraged cat, for example, will resonate with many people:

“The word ‘yew’ . . . when uttered as an explosive, is the Cat’s strongest expression of hatred, and a declaration of war.”

In 1944, Mildred Moelk revolutionized the world of cat language with her in‐depth study of the phonetics of the sounds produced by her own house cats. Her approach was to divide the vocal sounds of domestic cats into three main categories based on how they are produced. First, those made by the cat with their mouth closed, such as purrs, trills, chirrups, and murmurs. Second, the sounds made while the cat’s mouth is opened and then gradually closed—these include the meow, the male and female mating calls, and the aggressive howl. The last group are all made while the mouth is held continuously open, generally associated with aggression, defense, or pain in cats. They include growls, snarls, yowls, hisses, spits, more intense mating cries, and shrieks of pain.

The difficulty in this vocal categorization lies in the huge amount of variation in the production of sounds, both between cats and within the repertoire of a single individual. As Moelk so elegantly put it, “The house‐cat, unlike man, has enforced upon it no model of traditional language and no standard of correct pronunciation to which it must conform.” Her work has been used as the basis for the analysis of cat vocalizations ever since. Some investigators have attempted to classify them using phonetic criteria like Moelk, while others have examined their acoustic qualities or concentrated on their behavioral contexts.

Although cats have a huge range of vocalizations, in cat‐to‐cat interactions they generally reserve these sounds for three types of occasions: finding a mate, fighting, and communicating between kittens and their mothers. The first two involve supernoisy sounds that we tend to hear at nighttime. Caterwauling, shrieking, bloodcurdling noises—the sorts of calls that make you rush outside to identify the source or cover your ears to block them out. In their quest to communicate with humans, cats seem to have ingeniously worked out that it is the gentle sounds, like those used between a mother cat and her kittens, that appeal to us most.

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Newborn kittens start life with the ability to purr, spit, and produce a few simple “mew” noises. At least they sound simple to us. What sounds like a lot of squeaking to the human ear is actually a range of different kitten calls. In addition to crying when they are hungry, kittens have a distress call that varies in tone, length, and volume depending on the reason for their anxiety. The mew of a kitten that is too cold has the highest pitch; becoming lost from the nest produces the loudest mew; and the most urgent and persistent mew is reserved for when they are somehow trapped. This last cry often happens as the mother sprawls out on her side to allow her kittens to nurse, inadvertently lying on some of them in the process. Depending on the type of cry, she responds by retrieving the lost kitten or by changing her position a little. Shifting her body as she lies nursing her litter encourages a kitten that has dropped off a nipple and become chilled to snuggle back in, or enables a squashed kitten to wriggle back out. A study by Wiebke Konerding and co‐researchers looked more closely at the responses of both male and female adult cats to recordings of two different types of cries made by kittens. One type had been recorded in what the authors describe as a “low arousal” context, made by kittens that had simply been spatially separated from their mother and the nest. The other was recorded in a “high arousal” context in which, as well as being separated from their mother, the kittens were held by the experimenter (restrained/trapped). On hearing these recordings, adult female cats oriented themselves toward the source of the cry (a loudspeaker) faster for the more urgent (trapped) kitten calls compared with the less urgent (strayed from nest) ones, indicating that they distinguished between the two. This happened regardless of whether they had ever had kittens themselves. Male cats, on the other hand, although they reacted to the kitten cries, showed no difference in their reactions to the two call types. Female cats therefore seem somehow hardwired to identify distress calls of kittens. Studies have also shown that each kitten develops its own individual versions of these calls and that these remain constant as it grows older. Whether mother cats can recognize their individual kittens from their calls alone remains unknown. In turn, mother cats have a very special type of call they use when interacting with their kittens. Often described as a chirrup or chirp, this gentle trill‐like sound was written by Moelk as “mhrn”* phonetically. It is a delicate, cheerful sound, described by the nineteenth‐century writer Lafcadio Hearn as “a soft, trilling coo, a pure caress of tone.”

To humans this enchanting call sounds much the same in all mother cats. Kittens, though, can recognize the chirrup of their own mother when they are only four weeks old. They can distinguish it not only from her meows but also from the chirrups and meows of different mothers. Researchers discovered this by videoing and analyzing the responses of four-week‐old kitten litters when hearing vocalizations of their own and other mother cats. While a mother cat was absent from the room, experimenters played recordings of vocalizations from behind a screen to her litter of kittens still in their nest. They played them a meow and a greeting chirrup from their own mother as well as a meow and chirrup from an unknown mother cat, at an equivalent stage of motherhood to their own. Looking at the kittens’ responses, the researchers found that they became alert faster to chirrups than to meows. They also stayed alert longer, were quicker to approach the source of the sound (the loudspeaker), and stayed there significantly longer when hearing their own mother’s chirrup compared with any other of the sounds. That kittens can do this from such an early age suggests an advanced level of cognition at a time when they are only just beginning to move around and explore their world. This may be an adaptation for survival in the wild, where litters of kittens are often hidden out of sight by their mother while she goes off to hunt or find food. Her reassuring chirrup as she returns lets them know that it is safe to come out.

As kittens mature into adult cats and their vocal cords develop, their tiny mews gradually change into the more elaborate sounds that we describe as “meows.” I’d been studying my adult hospital and farm cats for a while before I realized, just like Galiani back in 1772, that I had never heard them meow to each other. They would hiss occasionally and may well have quietly purred when sitting together, but that was the extent of their vocalizations. Later studies confirmed this discovery—the iconic meow of adult cats is almost exclusively reserved for cat‐human interactions.

In the wild, away from the comforts of a human home, mew vocalizations gradually decrease as kittens become more independent. In house cats, though, meows are by far the most frequent vocalizations directed toward humans. Our pet cats often combine the meow with extra sounds such as trills or purrs. Some cats, like people, are chattier than others. Certain pure breeds, particularly oriental ones such as Burmese and Siamese, have a reputation for being more vocal. That said, many random‐bred house cats, or moggies, spend their days meowing hopefully at their owners.

So why do they meow at us? It seems that over the ten thousand odd years that they have associated with us, cats have learned that we don’t always understand their wonderfully subtle language of scents, twitches of the tail, and flicks of the ears. They need to make noise in order to get our attention. And lots of it. For the ever‐adaptable cat, what could be more logical than to use vocalizations that, as a kitten, so effectively achieved a response from their mother?

What exactly is a meow? A simple answer is hard to find, and it depends on who you ask. Nicholas Nicastro from Cornell University has studied the meow and our understanding of it extensively. His wonderful though head‐spinningly technical definition describes the acoustics of the meow: . . . a quasiperiodic sound with at least one band of tonal energy enhanced by the resonant properties of the vocal tract. The call ranges between a fraction of a second to several seconds in duration. The pitch profile is generally arched, with resonance changes often reflected in formant shifts that give the call a diphthong‐like vowel quality. . . . This call type very often includes atonal features and garnishments (trills or growls) that may serve to differentiate the calls perceptually.

A slightly simpler, more phonetic version comes from Susanne Schötz and her team in the Meowsic project at Lund University in Sweden: “. . . a voiced sound generally produced with an opening‐closing mouth and containing a combination of two or more vowel sounds (e.g. [eo] or [iau]) with an occasional initial [m] or [w]…”

Urban Dictionary’s definition is far more succinct but to the point: “Meow is the sound a cat makes. It is also the sound a human makes when they are imitating a cat.”

To the human ear, meows can sound friendly, demanding, sad, assertive, persuasive, persistent, plaintive, complaining, endearing, and even annoying. Some investigators have attempted to categorize meows into different subdivisions, but their classification proves tricky because, just like other cat vocalizations, the meow varies substantially among cats—and even changes in the same cat at different times. Despite this variability, there seems to be a word for “meow” in every language, from the Danish “mjav” to the Japanese “nya.”

However we choose to say or spell it, the sound of a cat meowing is unmistakable. Unless that meow you thought you heard is actually a baby crying? Both sounds are generated by the vibration of the vocal cords in the larynx, and the acoustics of the two are remarkably similar, particularly with respect to what is known as fundamental frequency, or the number of waves of sound that occur per second. To the listener this frequency is perceived as the pitch of the sound—the higher the frequency, the higher the pitch. The cries of healthy babies have been shown in various studies to have an average frequency of 400 to 600 Hz and are described as having a falling or rising‐falling pattern as the cry continues. Adult domestic pet cat meows, although hugely variable, were found by Nicastro to average 609 Hz. Other researchers, such as Schötz, have reported similar figures.

Pitched around the same level, both cat meows and baby cries seem to be particularly hard to ignore. The much‐researched cries of babies have been shown to elicit alertness and distress in adults. In fact, Joanna Dudek and coworkers from the University of Toronto demonstrated that hearing babies’ cries affects our ability to perform other tasks. No one has tested yet whether cat meows have the same effect but, given the acoustic resemblance to baby cries and the creativeness of cats, we can probably assume they are quite distracting.

Is this why cats are so hard to ignore? Have they somehow hot‐wired our brains so we simply must respond to an urgent need to take care of them like a baby? Possibly yes, but probably not intentionally. Throughout domestication, we may have unwittingly selected for cats with the most persuasive meows, those that tend to resemble the cries of our own infants. Nicastro’s study showed that compared with African wildcats (the ancestors of the domestic cat), the meows of domestic pet cats sound much more pleasant to human listeners. This may well be related to the differing pitches of their vocalizations, with the wildcat calls averaging 255 Hz compared with the much higher 609 Hz pitch of the domestic cats. Another study, exploring the acoustics of feral cat and pet cat meows, found the pitches of feral cat meows to be much lower than those of pet cats too. The meows of the ferals more closely resembled those of the wildcats in Nicastro’s study. This suggests that socialization and experience with humans in some way modifies the meows of domestic cats.

Interestingly, while feral cats barely meow at all when first looked after by a human, rescue workers often report that ferals increase their rate of meowing as they spend more time in their company. Even some of the feral cats that I watched on the farm, who only ever came near me very briefly when I dished up their food before leaving each day, gradually began to learn to meow a little as time passed. Cats learn fast.

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Sarah Brown’s The Hidden Language of Cats: How They Have Us at Meow is available from Dutton.