The "Elevator Butt" and the stiff tail (caution...rated R)

OK, so my wife tells me that everyone here has given a name to that little behavior that the cats do when they have their backs scratched by the tail as an "elevator" butt.

But what's up with that "stiffie" Andy gets. I'm talking about the tail that get's, well, hard and shapes into a question mark?

All my cats are fixed so I don't believe it's anything sexual, still it is a bit strange. Out of my 5 cats 3 of them get this 1 female and 2 male.

In a book entitled "Keeping a Cat" by Goumot, there's a whole page illustrating the meaning behind the tail. Your description means the cat is in a good mood, happy and wants to flatter you.