Due to their balloonish inability to feel pain, John collides with the ceiling harmlessly. He laughs hysterically as he rebounds towards Carrie, bodily tackling her and smooshing her up against the floor, causing much of the air from her torso to redistribute into her extremities.
That's when she decides to try something different. She tries to consciously change the air pressure inside her body, pulling it out of her arms and legs and back into her torso.
"What the heck are you doing?" John squeaks, holding her tight to the floor.
He is answered with a sudden push from her body as he is flung off of her. He bounces off of the wall before floating above her. She has removed all the air from her arms and legs, most of it going straight into her breasts. She can't help but giggle uncontrollably for several moments before normalizing her air pressure.
"Nice trick! But try this on for size!" John roars, which makes her giggle even more furiously. He kicks off of the ceiling, rocketing towards her once again. But she has another plan in mind, and this time she simply lifts her legs, positioning herself just in that right position as John's inflated penis lands squarely between her legs with the grating sound of (naturally) two balloons rubbing up against each other. It takes some time to fully insert as there is no lubrication between two balloons, just friction. Of course, now that he's in...
"Gotcha now!" Carrie laughs wholeheartedly. "You're stuck!"