At five years old, our cats are still relatively young, but both of them occasionally tune up with an apparently random yowl. It seems to happen most often when the yowler is separated from the rest of the household, and I have decided that these howls are demands for reassurance, or guidance to the nearest human.

Our cats don't meow at each other, only to us. They certainly communicate with each other, but not with the full-voiced MEE-IAOU that means "Do this thing for me right now", such as delivering the five o'clock treat, or the meeker mew that means "If you don't mind, I would like to exercise this privilege that you have extended to me in the past", such as drinking from the kitchen tap. Those vocalizations seem to be reserved for use with humans.

With each other, Watson and Isobel are largely silent, although they play together (sometimes quite violently) and spend hours snoozing together, often with Watson's arms wrapped around Isobel's neck. It has occurred to me that they might be conversing telepathically.