Press into her and see how she reacts
From Create Your Own Story
You move your cock up and down through the valley of her ass, giving a good feel of just how big it is. You her her let out a little "Mmm..." of approval. She presses her whole body back into you and continues to grind her ass against your cock.
"I had NO IDEA you were so well hung Archie. You've been keeping secrets from me! Bad boy!" she said, popping her booty up at the end for emphasis.
"Well, I had no idea you'd be so into it Veronica!" you say, still getting over your shock at what she's doing.
"Mmmhmmm..." she pulls away from you and turns around, appraising your cock approvingly "you certainly seem to be into me, BIG boy, so how could I refuse!"