So far, all of my cats do/did the same thing: when they are resting and you touch them from behind - I know you're not supposed to do that, but sometimes they are just too cute to resist - they would make this little sweet sound, something like "rrrrrr". Sounds familiar to anyone here?

Why do they do that? Is because they feel disturbed, or are they surprised? Or - since it sounds so friendly - is it their way to say "hi"?

What's your theory?

Kirsten