I have heard before that actually cats will purr when they are experiencing any extreme emotion, whether it be pleasurable or disturbing. I've had many cats who purr at the vet's. In fact, Big went for his annual last month, and Dr K couldn't even listen to his heart for his loud motor running! Of course, Big isn't the best example, because unlike most cats, he doesn't find the vet to be all that distressing.

I've had two cats that don't purr at all, at least not audibly. Boosie (rainbow bridge) would seldom purr, and even then you had to be in a quiet room with your ear to her chest to hear it. But she was not an unhappy cat.

Cookie is about a year and a half old now, and I have yet to hear her purr, although she is a very contented little girl.