Before Erica had a chance to react her sister had snatched the bottle out of her hands and turned it on her. Maria, growling and baring her fangs quickly sprayed her sister. Maria sprayed her sister's chest, face, and crotch vigorously, then tossed the bottle aside and waited for Erica's transformation to start.
"Let's see how you like it." She sneered, her new canine muzzle making it hard to talk. Maria felt her tail lashing back and forth behind her, and her new testicles weighing heavy against her thighs. She didn't dare see what would happen if she sprayed more of the stuff on her. Instead she'd just watch her sister suffer the same fate as her.
Erica tried wiping as much of the stuff off her as possible but it was too late, and the changes had already started. Holding her sides, Erica kicked off her shoes and then her skirt and panties. Her crotch felt so hot, and uncomfortable. Maria snickered as she saw her sister's tiny clit swelling like a water balloon. Her vulva was engorged as well, as her lips sealed completely.
But then Maria stopped giggle as she watched Erica's clit swell larger and larger, far bigger than her own. The shape was different too. Rather than take on the pointed, and dark red color like her cock, Erica's seemed to be getting darker. Almost black in color. And the end wasn't pointed, it was flat, and had these weird ridges along the edge. Large softball sized orbs dropped into Erica's newly formed scrotum, and instantly bulged. Maria noticed how Erica's inner thighs were covered in a thin layer of brown hair, and how they appeared to be more muscular.
"It's...too tight!" Erica gasped, tearing off her shirt. Maria took a step back as Erica's body nearly doubled in size. Muscles and hair grew, and Erica's body became obviously male. Her jaw was hard, and her nose seemed almost swollen. The nostrils were large and Erica's chin was covered in bristle like whiskers. She cried out in pain as her face suddenly surged forward. Her ears stretched to the top of her head, and her face completely reshaped into an equine muzzle. Maria watched fearfully as Erica got to her feet. Her sister was now two feet taller than her, had muscles the size of footballs, and had a large horsecock and balls dangling from her crotch.
"I dobe ur abby ow." Erica huffed, her words coming out even more slurred as she grew accustomed to her new mouth.