A couple years ago, my mother’s cat, “Toaster”, was put down somewhere in her mid-teens due to her developing a brain tumor. We don’t know exactly how old she was; my mother adopted her from a sober living house where she’d ended up after her original owner had died, and we thought she was somewhere around 15 or 16. Somewhere around a year or so before her passing, I was visiting my mother’s apartment and Toaster was sitting in my lap, and as I was stroking her I noticed something I’d never seen another cat do before - if I stroked or scratched her lower back right above the base of her tail, she would immediately start licking her lips, and as soon as I stopped she’d stop. After I went home that night, I immediately went up to Ebeneezer, my own cat, who was 5 or 6 at the time, and tried it on him. It didn’t work. I wrote it up to it being some weird tic of that particular cat and didn’t think about it thereafter.
That was, as I said, a few years ago. Ebeneezer had his tenth birthday a few weeks ago, and as I was petting him a few days ago I suddenly discovered that he had suddenly developed the same response! If I scratch him in that spot, he starts licking, though he doesn’t lick the air like Toaster did - he’ll either lick around his chest and shoulders, or, if he’s in my lap and my other arm is within reach, alternately lick and gently “nibble” on my arm (he opens and closes his mouth on it, but doesn’t use his teeth). I’ve read that most cats dislike having their lower back petted or scratched, but just like with Toaster, it doesn’t seem to bother him - I’ve even noticed him start to purr while I’m scratching him there, and he doesn’t make any attempt to get up or go away if I stop.
Does anyone know the straight dope on why this happens? I’ve tried Googling the phenomenon, but I haven’t found anything authoritative - just other people relating similar experiences with their cats and offering guesses as to what’s going on.