More cushion for the pushin

You approach her from behind and you kiss her back (because of the height difference), with one hand wrapped around her waist and the other caressing very bulbous booty (new size being increase by 2 inches). While massaging her butt you gave it a nice quick slap and her giving a surprised and aroused gasp, with your hand still on it you feel it grow another 2 inches. The fabric warping and creaking more as it grew making that faint panty outline more visible "Oooh I like where this is going" she said with a slight quiver in her voice," Let's turn this pillows into mattresses" you give another spank for another growth now making her legging see through.