The same friend once sent a link to a video that my cats would enjoy. (They did, at least the one who was sitting in my lap at the time.) Nothing thrilling for a human, just various numbers of mice crawling over the screen at random. In subsequent discussion, it turned out that the mice weren’t just moving around in absolute silence; they were squeaking. I couldn’t hear it.
Side expeditions to assorted online hearing tests reveal that at some time when I wasn’t paying attention, I have lost my high-frequency hearing. It cuts out somewhere around 10k; exact numbers will have to wait for professional assessment. This is unnerving.