Faye giggled excitedly as ideas flooded her mind. While she rummaged, she quickly drank a portion of the breast growth vial and replaced it. She then set aside the mixing beaker and held the two vials she was searching for. Originally she would have just tried the male vial and hope it would give her a dick, but now she could take it a step further and she remembered the old saying. 'In for a penny, in for a pound.'
She poured the full contents of the vial labeled horse and the penis growth vial into the beaker. Her heart was pounding in her chest with anticipation. As the originally clear liquid turned blue Faye smiled. By this point, her chest was starting to heat up as her shirt grew tighter. The breast growth vial was starting, taking her modest B's to small C's
Faye quickly downed the concoction and stowed the contents away to hide them from Mary
"Mary. She'll probably try to take this away from me. She is always spoiling my fun," Faye frowned. "Maybe I need a little more leverage on her." Faye held up the muscle growth vial and swallowed a fourth of the contents.
"Faye are you down there?"
Faye opened the bedroom door and stepped out. "No, I'm up here silly."
Mary, still naked, was a head shorter than Faye currently was and still growing at a very slow rate. "What were you doing in there," Mary asked.
"Giving myself a better chest to go along with this bitchin body," Faye struck a pose and then cradled her swelling chest.
"Well I cancelled out my email so hopefully no one else will be coming. Can't have a dozen people coming here to watch this whole affair."
"Aww, is little Mary shy someone will see her?"
"Yes, and so should you. What will people think if they saw you now?"
" 'Damn that girl is huge'?" As if to emphasize her statement, Faye's shirt tore down the front thanks to her expanding breasts. But what really got her attention was the tingling in her crotch.
"Faye I'm serious!"
"Why can't you just enjoy something this awesome? You could be anything you ever wanted. Even look like one of those monsters you're so fond of looking at."
Mary turned away to collect her thoughts and missed Faye's face flush with pleasure as her panties began to dig into her skin as something expanded inside them.
Mary finally turned around, her height actually passing Faye's now. "I don't want you to get hurt. I almost got trapped as a doll if you hadn't shown up. What if you drink something that causes you to loose all your limbs and can't get the vial open? Then what?"
Faye shrugged. "Then I'll just keep adding stuff to myself and try not to remove anything. Besides, you can't say that this," she heaved her now F cup breasts up, "doesn't look great." Faye moaned as the mass in her panties suddenly surged forward.
"....yeah, they do look pretty nice," Mary admitted.
"Plus, you haven't seen nothing yet. Check this out." Faye motioned to her crotch and waited for Mary to realize what she was watching.
Beneath the folds of the ruined pants, Mary was able to see what looked like her sister's vagina inflating in her panties.
"You grew your vagina? Why?"
"No silly, but that might be next, just watch the show."
Mary watched the mass in Faye's underwear expand, taking on a more distinct shape. "No way. No freaking way." Mary backed off as the mass continued to stretch the fabric to it's limit and beyond. When the mass reached the size of a baseball the straps gave way and launched the underwear past Mary's face. It took her several long moments to register the fact that hanging between her sister's legs was a horse cock and balls. And they where still growing.
"What the hell did you do?!"
Faye shrugged. "I wanted to see why men were so obsessed with sex and thought of this."
"But a freaking horse cock?!"
"Hey you've heard the saying hung like a horse. I wanted to be literal."
"What about your job? I don't think there's an office that can hire 7' tall horse women."
"Who said anything about me stopping at 7'? I wanna go big." Faye shook her hips and let the expanding dick sway between them. While Faye's breasts seemed to stop around H cups now, Mary also seemed to stop growing around 8'3". "And besides, you aren't exactly small Mary."
"I was trying to get my height back to normal and...and....and how big is that thing going to get?" Mary asked, her face flushing. All the changes she had gone through had made her very horny and she didn't want to admit that the thing growing out of her sister was starting to look inviting.
"Why? Interested?" Faye reached down and ran a finger down the length of the now 9" shaft. The skin at the base had toughened up and darkened to a deep brown color, forming the sheath. Hanging between her legs was a pair of baseball sized testicles in an equally dark colored ball sack. The shaft itself was pink at the flat, flared cock head and mottled brown spots near the base.
"N-No! Why would you ask suck- I mean such a thing?" Mary blushed at the slip.
Faye pointed at Mary's still naked crotch and added, "I think your body is speaking for you sis."