If we scratch our cats at the base of their back, right next to their tail, they raise their butts in the air and lean forward.
If we scratch it’s shoulders it doesn’t really raise its shoulders in the air.
My friend said that they get off on having their back scratched right next to their tail, but I’m not too sure about that.
FatDave
Nice observation. We call it ‘elevator butt’ and I think almost every cat does it. I guess they’re just more sensitive near the base of the tail.
That was your question, right?
Yes, I guess that was my question…
Now, as for sensitivity near that location, does that mean it just feels “good” to them, or they are aroused by it? 
My cats are neutered (aka they have no balls) and they still like it, so I assume it doesn’t arouse them per se.
I personally think I’m helping them to masterbate when I do that.
Both of my males and both of my females love it, so I don’t think having testicles has anyhthing to do with it.
That’s odd… With all the cats with whom I have cohabited (perhaps a dozen. No, not all at once), I have never once noticed “elevator butt”… But they all of them, every last one, had “elevator shoulders” if you scratched them right at the base of the neck.
Well Chronos, you’re supposed to scratch them above the base of the tale, not below it. Now go wash your hands. 
I always thought it had something to do with scent-marking. When my cat is partrolling her space, she rubs her face against things, and she walks under things and rubs her tail up against it.
Aah, here’s a web site that says that cats have scent glands at the base of their tail:
Scratching the cat at the base of the tail gives it a good sensation and nothing sexual, but they just love it. Some go wild, like one of my cats does, and others just get elevator butt and obviously enjoy it, like my other cat does. There are sensitive nerves there and along both sides of the flanks. Scratching your cat there is doing his a great favor and he/she loves it. My one cat acts like I’m tearing her butt off with all of the wild squealing, flopping around and all, but she comes back for more and doesn’t run away and purrs her butt off afterwards.
Cats have glands on their cheeks that they use to mark people and things with as friendly and theirs. Your cat rubbing her or his face on your pants cuffs is his or her way of marking you as THEIRS for all other cats to know. You are one of their pack. Plus, most cats enjoy having their cheeks and chin stroked because it is a sign of affection among cats.
I don’t know about anal glands, but cats have the ability to piss backwards with a special piss used to mark their territory so that any cat wandering by can tell what cat is there, what age he or she is, how healthy he or she is and how long ago the place was marked.
Our cat does that too. I just assumed that it was because cats scratch with thier back legs and can’t scratch themselves there. It’s just like someone scratching my back. I love it. I don’t get elevator back, but I’ve been known to groan and been nice to the kind soul who scratchs it for me.
If you scratch our one cat at that spot, he elevates his butt, looks at you, and then falls over. Every time. It’s hilarious!
Jman
i have experienced the same thing, except with my dog. whenever i pet his but, his legs go all stiff and its hard for him to walk.
CALTITUDE (kal’ tih tood) n. The height to which a cat’s rear end can rise to meet the hand stroking it.
Funnt thing here, we do something called pussy patting anyway, lightly pat your cat on the rear above the tail, same spot you scratch at. Some cats will not like this, some will though, most do. As a matter of fact, some like a flat out wallop. My cat can not get enough of it! So start slow, and go harder, anyway, oddly, my cat is to the point that if a humane society employee walked in on me, I would probably get taken away for animal abuse or something, my cat is a female, and she simply can not get swatted hard enough, literally to the point where her legs collapse under herslef from the pound. I assure you, pure pleasure is what she is in, if I stop, she will come up to my face and swat me back, claws and all, untill a resume. It is truly bizarre, I find most cats love this for some reason
If you stroke a cat from the shoulders all the way back, it is funny to see how the tail goes up as your hand moves back. It seems almost as there is a mechanical connection. When I was a little boy I was told the cat raises its tail when you stroke it so you will know where the cat ends. At the time it made sense to me but I was only 6 or 7. I thought people may continue to stroke past the end of the cat Everything in nature must have a good reason for being so.
I remember reading that elevator butt was a throwback to kitten days - an invitation for Mama Cat to examine Kitty’s anal region.
Simon
We have three cats (all three fixed): One male gets elevator butt, the other two, a male and a female do not.
But the one that gets it–you should see the look on his face, pure exstasy.
TV
I recall reading somewhere (can’t remember source) that mother cats lick at the base of thier kittens’ tails to stimulate defecation. This may be part of the “reversion to kittenhood” behaviour that features in a lot of cat/people interaction. (i.e. cats behaviour in cat/people interaction is in many ways similar to kitten/mother interaction. This is common in many domesticated species, where the animal retains many juvenile behaviour patterns.)
In female cats, that’s the spot the male places his paws when copulating.
Or so I was told. I dunno if that’s actually relevant.
My dogs react more than my cats. The female dog will get really playful and woofy if you scratch above her tail. The male dog just gets that “pleasure” look on his face. The cats seem to like it, but prefer a scratch behind the ears or under the chin.