Why, when you pet a cat from head to tail, do they lift up their little tookus' as your hand gets there?

I think it is to help finish the pet with the most frictional contact.

It’s a sexual thing, I think.

Me-ow.

The base of the tail is one of several locations of the cat’s sebaceous glands that produce its scent markers. These are the spots that it likes to rub against objects (and friends) to leave a scent signature. Others are located on its chin, shoulders, lips and temples, all of which it also likes to rub.

But cuteness is definitely a survival trait in cats.

I bet the scratching feels good, almost life a massage. I do a scratching motion down my cats’ backs and they love it. Tails up! = ^. . ^ =

purrr…

kitty orgasm

I always scratch my cat on his back right where his tail starts.He will lay the front part of his body down, close his eyes and poke his behind and tail straight up. It looks like he’s having “the big O”. It cracks me up.

Always pet a cat in the direction of its fur, and be aware that the spot just above the tail is sensitive – some cats adore being scratched there, others hate it. If your cat suddently nips you while you are petting it, it may be because he’s “overdosed” on the pleasurable sensations: some cats can tolerate only a few minutes of being petted, while others will happily doze in your lap, being stroked for hours.

Source.

I have no idea. I thought my cats were the only ones who did that. I thing it’s adorable. Especially when they purr a lot.

Have someone run their finger gently down your spine, feel yourself do the same thing (or at least something similar).
It’s great for foreplay, my ex used to LOVE it when I did that to her

The cat’s nervous system is really stimulated.

when i scratch my cat’s back above the tail, he seems to enjoy it at first, and then he looks around, and finds something to lick. then after awhile, he starts nibbling it. i think it pisses him off after awhile, but it’s so goddamn funny.