"A" being the beginning - where one starts in their butt stuff, how they should start simplest like the Fun Factory Bootie. Ease into it while easing it in, folks!
B Balls cause there are 2 of them, otherwise it'd be called "A Balls" corresponding to 1! It's also the second letter, signifying the next step in your anal expedition.
Not only that, it also has a jiggling sensation for when you do the shimmy while the B Balls is up your bum!
Now, do a little shiver... and a little quiver... shimmy with me!