Mary upends the vial and chugs the contents down quickly. Why go only part way? Go all the way and have the most fun!
The liquid splatters and flows down Mary's hollow body, coating and becoming absorbed. It doesn't take long for the liquid to work. Mary's body darkens to a shiny blue-gray. Her belly gurgles and Mary has the urge to burp, but can't see to make it happen. Her whole body thickens and plumps out. Both of Mary's arms and legs seem to balloon the fastest, gaining width and making them look stubby and short.
Mary's once pristine breasts dissolve into her body while her shapely hips become exaggerated, filling up and out. Her bottom is wide and getting wider. It sticks out comically. Mary pats her plump bottom and giggles as a tail 'plunks' out. Mary feels quite ridiculous, but is enjoying it immensely. Soon, her belly and torso swell to match her giant hippo bottom. Her new width forces her onto all four new legs. Hands and feet widen and merge flawlessly with her legs.
Human ears pull out, shrink and move to the top of Mary's head. Nostrils widen and flare to match a widening snout. Mary's eyes move further apart and to the sides of her head. Finally, two teeth grow down from Mary's rubbery mouth.
Mary, now a complete inflatable hippo, tries to move around to get a look at herself, but as she turns, she bumps into the wall unexpectedly. As she changed, she grew to a massive size. Mary now fills almost the entire room!
Sitting down on her inflated haunches, her bottom flaring out even more, Mary ponders what to do next.