Cats, in all shapes and sizes, in all degrees of character, and in every perceivable habitat, represent an integral part of human existence. Nearly all cat parents can attest to one fact. Whenever your beloved ball of fur starts sounding like a high-quality trimmer on full blast, that makes anyone within the vicinity go “awww” in unison, with a little bit of “isn’t he adorable” and a sprinkle of “I think he likes you” thrown into the mix. All in all, purring can bring out the nurturing instincts of humans. But, when one of their distant African cousins decides to roar, on full blast (given ideal conditions), a lion’s roar can be heard 8 kilometers away. Putting that into a Sri Lankan/Colombo context, if a lion decides to roar from Liberty Plaza, you should hear it around the Dehiwala Flyover. Upon hearing such a roar, everyone within proximity would be going, “Oh my God! We’re going to die” or “I should have worn my brown pants” and all that.

Naturally, purring has become an overused (but beloved) cliché in most aspects of life. Mechanics and motor vehicle aficionados speak of how a finely tuned, meticulously designed engine can “purr” into life. Some know how to “purr” the right way, to get what they want. All these things, prove one thing: imitation is the sincerest form of flattery that mediocrity pays to superiority. I’m pretty sure Oscar Wilde was looking at his cat when he came up with that absolute banger of a quote. Cats are superior like that, and that’s a fact.

So, now it’s time for us to channel our inner 4-year-old because it’s time to ask the right questions. What is purring? What is roaring? What’s the difference? Why am I reading this instead of attending to my deadlines? Well, let’s find out!

Let’s turn our attention towards purring, first. Our journey starts with the hyoid apparatus. Apart from having a name that looks like a vowel salad, the hyoid bone is the part of the feline anatomy that helps with their distinct vocalizations. It supports the tongue and larynx (voice box) and is shaped like the letter “H,” which forgot to duck when going under a low beam (bent H shape). Humans do not have a hyoid “apparatus” as such, but a single hyoid bone. The hyoid apparatus, on the other hand, has nine components (Pérez et al., 2010).

Now, let’s take the majestic lion, the supposed “king” of the jungle (no self-respecting “king” would sleep close to 20 hours a day, ambling around, and yawning wide, while the lionesses do all the work) as an example. Now the hyoid apparatus that is found in a lion, happens to be incompletely “ossified.” As in, it’s not a collection of several solid pieces of bone banded together. One component, especially the epihyoid, if we are to be specific, is ligamentous (think of two chain links connected by a flexible band).

Because the hyoid apparatus is incompletely ossified in the Panthera genus (The genus to which Lions, Tigers, Jaguars, and Leopards belong), it allows for more space for the vocal tract to be elongated. Which, in turn, means more area for air traveling through it. Plus, their vocal cords (or folds, to be exact), are square, as opposed to the triangular-shaped vocal cords found in humans. Because of these specific anatomical arrangements, they can roar, without exerting much effort from the lungs. But, they can’t purr. Also, a lion’s roar on full blast can clock somewhere around 114 decibels. Because anything above 85 decibels is deemed hazardous to humans, maybe a lion roar isn’t the best thing to use as an alarm tune.

When you consider cats like fishing cats and jungle cats (or as the above image depicts, a caracal), they have a completely ossified hyoid apparatus. That is, the epihyoid is not ligamentous and is rigid. This, in turn, paves the way for a comparatively shorter vocal tract as compared to the Panthera genus, which in turn makes them incapable of roaring, but capable of purring. When air passes through the vocal cords of a cat, it causes the rigid hyoid apparatus to resonate (like a tuning fork. Or just hit your head with a rice cooker lid, same effect), which in turn creates a low-frequency rumble, which is what we call, purring. This can happen when they inhale and exhale.

Also, this anatomical arrangement gives them the ability to make some truly adorable sounds (like a cheetah’s adorable meow or the “disgruntled Donald Duck at Pettah Market” vocalizations that fishing cats make), which in turn makes us forget for a moment that these are apex predators in their given ecosystems and we are nothing but walking meat bags to them. So go all googly-eyed at a reel on your phone and croon all you want, but leave them be and respect their space, everywhere else.

Those of the Panthera genus were called big cats based on their ability to roar. The rest, who can purr, were classified as small cats. Now even the most visually challenged person can see that a cheetah and a cougar (Puma, Mountain Lion, etc, Not anything else! Tsk tsk tsk…) are “big” cats. But because they got the evolutionary short straw, they can’t roar, so they are not classified as big cats.

As with everything, there are exceptions. In this case, it happens to be snow leopards. Even though they are classified as big cats and put in the Panthera genus (which has more to do with cranial features and will be something we’ll cover in a future article), and even though they have incompletely ossified hyoid apparatus, cannot roar. Instead, they are known to make a non-aggressive puffing sound called a “chuff.”

The exceptions don’t end here. According to recent studies, even big cats like lions and leopards are known to do a version of a purr, only during oestrus (when they’re ready to mate and start to ovulate), and during copulation (when they are mating). Then came the claim that those vocalizations cannot be stated as true purring, but are variations of other vocalizations attributed to them (like gurgling or growling, which can sound like purring). Remember how we told you that purring can happen both during inhale and exhale? Well, some experts put forward a claim that supposed lion and jaguar “purrs” only happened during the exhale, so no chance!

Biology is an exact science, which is built on exact classification. So, there is no room for any ifs and buts. If there are any ‘if’s and ‘but’s and ‘how in tarnation?’ then it paves the way for another way of classification. That’s how it is and will be. So, if there is the tiniest bit of deviation from what is considered true purring, then it is not purring. So, what biologists today agree on is that only the families Felidae, and Viverridae, are capable of true purring. This will be so until some other discovery brings forth a whole new perspective. That is the beauty of science, where the only constant is change. Change with the times, change with the knowledge.

So the next time your cat purrs to psychologically manipulate you into giving it more treats, you know what happens inside that fluffbox that you love so very much!