I provide my answer because, to the best of my knowledge, there is no authoritative answer to the question: “Why do cats do silent meows?”
We therefore have to work it out for ourselves. If you research the question on the Internet, the first two listed results on Google search produces very poor answers. The third gives a hint as to what I believe is the answer.
We, as humans, expect a domestic cat to produce a sound when they open their mouth. We are expecting a meow. It is my view that from the cat’s perspective it is not obligatory to produce a sound under certain circumstances when they open their mouth.
The silent meow is really a form of body language. That is the point I’m making. It is body language that is understandable by other cats and after reading this article understandable by humans as well! Incidentally, I am assuming that cats direct the silent meow at other cats. This is not certain because the genuine meow is directed at humans only.
If you think about it, humans also open their mouths without producing a sound under certain circumstances as a form of body language. What about the look of surprise with the mouth slightly open. The look on a person’s face when they are aghast at something that they are seeing. What about the almost silent whisper in which words are mouthed rather than actually spoken. These are human versions of the feline silent meow. There are others.
So what does the silent meow mean? What is the cat trying to communicate? We have to rely upon our gut feeling together with the circumstances under which it is made to figure this one out. My feeling is that it is a form of close communication by which I mean it is made when we are in close proximity with our cat. It is a friendly form of communication much like a friendly greeting or a friendly recognition of our attention and presence. and a sign that our cat likes to be in our presence. In short, it’s a friendly signal which has a bonding effect. It also gets our attention. We observe it and respond to it. It works.
There may be an element of laziness at play. The silent meow requires less effort than the full-blown auditory version.
Incidentally, my cat’s silent meow sometimes has a slight chattering at the end of it; a slight modification, let’s say. Elliot (the cat in the video) has a silent meow with a slight non-meow sound at the end.
One last point: the purebred cat which is most prone to producing the silent meow is the British Shorthair. They are genuinely completely silent.
When I stayed with the world famous cat photographer, Helmi Flick, her two British Shorthairs frequently communicated to me with a silent meow. It was very striking and noticeable. They were very delicate and elegant silent meows.
I am sure that the amount of times the domestic cat produces a silent meow depends wholly upon the cat’s own personality. It will be an individual characteristic although it exists, as we know, generally amongst the domestic cat population.
Those are my ideas at the time of writing this article based upon my personal experiences. If you know of a scientific journal which has published information about this feline characteristic then I would be pleased to hear about it in a comment.