By pure chance, Mary saw that Jess had picked out the Cow vial. "I was hoping to try a different vial," Mary said to her friend. "This was the first vial that I used. But you haven't seen it yet, so here it goes."
Mary was just about to drink it when she remembered what happened the day before. Just a few sips of the Cow vial had made her pass out for the entire day. But the Female Human vial had much faster effects without making her groggy. Either the vials all had different side effects, or her body was quickly getting used to transforming. In either case, Mary thought she should dilute the formula.
"Wait right here. I'm going to try something." Mary hurried from the room and soon returned with a glass of milk. "This vial knocked me right out yesterday," she explained as she poured a small amount of the vial's contents into the glass. "Maybe if I weaken the dosage I'll be awake to experience the transformation with you." Then another thought crossed her mind. What if she put a few drops of the Female Human vial into it as well? Perhaps it would also boost the chances of her staying awake, and the transformation not hitting her too harshly. "Okay, some experimentation is in order. You're going to love this," Mary smiled as she let three drops of the Female Human vial fall into the glass. Jess was eying her friend closely, probably wondering if Mary was losing it.
Mary quickly gulped down the milk. Somehow it tasted better than any milk she'd ever had. She drank it so quickly a stream of the white liquid was trickling down her face and neck. When she was finished, she wiped her mouth with her hand and looked at her shirt. "How clumsy," she giggled. She put the glass down on her dresser while patting her belly. Just one glass seemed to have filled it very satisfyingly. It was also beginning to feel very warm.
"How long will it take?" Jess asked, skeptically.
"I'm not sure. The change to a cow took an entire day, as far as I know. But I was asleep, so maybe it was much faster than that. Changing back to human and taking a double-dose of the Female Human vial to get this figure took no time at--OH!" Mary fell to the floor, clutching her stomach. It felt like it was bursting. A massive pressure was building up inside it and stretching her body to its limit.
Jess knelt beside Mary, holding her shoulders. "Are you okay? Is something going wrong?"
"I'm not sure...," Mary gasped. "It's...probably the...udder..." Her waist was beginning to strain painfully and she fumbled with the button. When it was off, her zipper tore itself apart as a bulging belly came springing out. It continued to expand as the pressure inside of it grew and grew. Strangely, though, it didn't seem to be the udder that she had expected. It wasn't turning a pink color, nor was it growing teats. It felt much more firm than a sack of milk, but it was just as heavy. It pushed on her pants as the open waist clung tightly to her hips.
Jess stared with eyes wider than Mary thought possible. "Omigod, I can't believe it! I can't believe it!"
Mary was excited for Jess, though she was mildly concerned about just what this thing attached to her belly was. Besides that, however, she could feel other changes coming on. And Jess could already see them happening.
A new pressure on her head alerted Mary to two new growths. She felt horns pushing their way out from just above her temples and curving slightly inward. Her ears felt like they were being stretched like taffy. A familiar feeling in her butt told her that a tail was growing in. Then her bra started feeling tight.
Much of this was new to Mary. She wondered why her changes were so different this time. Could it have been the milk? Or were the changes always randomly assigned to different parts of the body? She didn't have much time to ponder these questions, as her breasts were now swelling painfully within her bra that was already constrained thanks to the effects of her first Female vial usage. She tried to unclasp the straps, but for some reason her fingers weren't able to get a hold. She looked closely at them and saw that her fingers were actually melting together. Now she only had two fingers and a thumb on each hand, and they were growing white fur that traveled a short distance up her arms.
Her feet shifted in her socks as well, but Mary was more concerned about her growing tail. She was regretting not removing most of her clothes before drinking that glass of milk because it would have avoided most of this trouble. "Jess, help me...get these...pants off!"
Jess grabbed the waist and yanked hard. Mary screamed at the pain of her cuffed tail slipping free, but it only lasted a moment. Jess removed her pants all the way as Mary sighed in relief. "Now the bra, please," Mary asked. Jess couldn't keep a bewildered look off her face as she followed the cow-woman's orders. She slipped her arms underneath the back of Mary's shirt and tried to removed the clasp, with a bit of difficulty. The way her breasts were expanding they were causing the straps to tighten against her skin. The fact that Mary's hair seemed to be growing and constantly flapping into her face wasn't helping Jess' efforts.
Finally, Mary felt her bra loosen and her breasts swinging free. They made very distinct impressions in her shirt and looked comically large. She poked one through the fabric and realized that they were full of milk. So what happened to her udder?
The changes were passing now, and she looked down at her massive belly. It was protruding by eight or nine inches, causing her shirt to ride up significantly. It was pert, but heavy. As Mary ran her strange new hands over it, she felt something moving around within. She gasped.
"You practically look like you're pregnant," Jess said in a half-joking, half-disturbed way. Mary, still sitting on the floor, glanced up at her friend in a look of shocked confirmation.
"What? But...no. No, that's impossible!"
"I guess this is what happens when you mix the Cow and Female Human vials...," Mary said. She slowly picked herself up off the floor. It was a bit more difficult than she realized, seeing as her body contained the added weight of two glands full of milk and what appeared to be an almost fully-developed fetus. She had some trouble standing, but made it to her full-length mirror.
Her hair had grown again. Now it was down to her knees, fuller than ever--and oddly enough--pure white. Two gray horns sat atop her head next to long cow ears. Her hands and forearms had grown fur, as had her feet and ankles. Her feet had only two giant toes on each foot, tipped with black hoof-like nails. Her white and black-spotted tail ended with a white cuff just below the tips of her hair. Two large breasts tented her shirt, which wasn't nearly big enough to cover a third-trimester pregnant belly.
Mary turned to Jess in a sheepish grin. "So...which vial do you want?"