Your cat companion may well do it: the silent meow. Your cat opens her mouth but no sound comes out of it. When I visited Helmi Flick and her husband in Fort Worth, Dallas, Texas I met, for the first time her two British Shorthair cats and also for the first time I saw the silent meow in action a lot of the time because the British Shorthair is well-known for the silent meow.
Sometimes you'll hear the faintest of noises emanating from the mouth. I have found a video of it on YouTube.
It's completely normal but when you first see it it looks a bit abnormal. You might even think something is wrong but no. It is said that the adult domestic cat only meows at us - people, but never with another cat. I'm not sure that is a strictly true behaviour pattern but it might be.
Assuming that it is correct then I wonder whether the silent meow is only ever directed at people. If it is then it is a learned behaviour from thousands of years of living with people. I wonder how they learnt it ;). It seems that some individual domestic cats realise that they can communicate with us without making a sound and they are correct.