Continued deep-throating

Amy was amazed:
For one thing, because just a few minutes ago, Sarah had been gagging on just the first few inches of Adam's spectacular boner. But now her best friend eagerly continued to deep-throat her brother's jumbo package like a pro, even without her help. Amy had no explanation for that sudden change, but neither did she really care, and instead excitedly cheered her on: "You go girl!"
And for another thing, what was even more amazing: Amy had just seen Adam have his second unbelievably strong orgasm within a short time, yet his shaft was still very much hard. In addition, the amount of cum Adam was able to shoot out was unreal. On his first climax, Adam had literally showered the girls with his yummy load. She could still feel the sticky substance all over her hair and her bust-line. And after his second climax, with his member buried balls deep in Sarah's throat, Amy saw that Sarah's tummy bulged out considerably. Evidence, that Adam had pumped an incredible amount of sperm straight into his sisters stomach.

Despite that powerful second climax Adam was still very much ready to go. When he stood up from the bed, with his sister kneeling in front of him, the blowjob slowly turned into a more violent throat-fuck, as he began rocking his hips back and forth,
Thanks to the ample supply of "Growth X" powered sperm now inside Sarah's body and stomach, her transformation progressed further, so far though without any visible changes, and thus none of the teens noticed this, and all of them were none the wiser.
With every thrust, Adam could feel his sister's throat giving leeway, so that he could easily plunge in balls-deep, only for the throat to tighten up again, applying more and more incredible pressure on his meaty pole. At the same time, with every thrust, Sarah had another small wave of pleasure ripple through her body.
When Amy looked at their faces, she saw that both of them had their eyes closed and that their facial expression were showing pure bliss and pleasure.
Both siblings were in heaven.

Every now and then Amy could catch a glimpse at a few inches of Adam's fabulous and heavy rod, which was slick and wet with saliva, before he forcefully plunged it back down Sarah's throat again. And every time the base of his shaft appeared again, Amy wondered, when her best friends big brother had turned into such a hung and powerful stud, with the biggest and most amazing fuckstick that she had ever seen. The shaft huge, hefty and thick, his cum like ambrosia. And why she had never noticed it before. While she had no answer to these questions, she knew that she was by now very, very eager to get in on the action.

And for that she needed to get Adam's attention.