Mary watches in unconstrained curiosity as her belly begins to swell. Pressing her hands to her belly, Mary can feel the pressure as it balloons outward.
At first, Mary's belly is a slight bulge. Then a good paunch. And it keeps swelling. Mary soon has a round potbelly, but instead of it pressing downward, like fat would, her's stands out pertly. She pats it and realizes it's air. Amazingly, Mary watches as her belly keeps ballooning. It looks like she's swallowed a balloon as round and pert her belly is.
Putting her hands over her belly, Mary feels it swell large enough that she begins to look very pregnant.
Soon, the swelling stops. Mary has a good beachball sized belly full of air. Rubbing her hands over the taut flesh sends shivers of pleasure up Mary's spine.