Mary pulled out the cow vial. She figured she would take one half now to get the changes started and the other half when Xander returned.
She eagerly sipped the sweet room-temperature liquid out of the vial and waited...
At first nothing happened. Then she began to feel a slight tingling all over her body. It was so faint she could barely separate it from the beating of her heart, but it was definitely there. She could also feel a slight pressure at the base of her spine...
After a few minutes without any noticeable changes, Mary decided to watch some television to pass the time. She sat on the couch and began flipping through the channels. She stopped on a documentary about the dairy industry. For some strange reason she was entranced by the thought of being milked.
Her eyes glued to the screen, Mary blushed as she felt a new wave of heat pass through her abdomen, and the tingling momentarily grew stronger around her chest. She looked down and noticed that her nipples were incredibly hard, and her breasts felt unusually sensitive. She blushed even harder as two wet spots began forming on her shirt.
"Oh, looks like the changes are starting", she said to herself, "Guess I should get myself ready". She removed her shirt and bra, closed the blinds in case any nosy neighbors happened to walk by, and then wrapped herself in a fuzzy blanket to keep from getting cold.
By now the tingling had gotten stronger around her face, ears, and feet, but no changes could be seen yet. A heat emanating from Mary's crotch made it difficult for her to sit still. Her breasts seemed slightly larger than usual, and her jeans were getting tight.
Another hour went by, yet no other changes had occurred. Mary was getting a little impatient. She got up to take another look at the instructions on the vials when felt an unusual draft against her tailbone. Turning around, Mary found a short cow's tail snaking out of the back of her pants! A small tuft of fur came out of the end like a paintbrush. Mary squealed in delight.
She removed her tight jeans to make room for the new appendage, and was surprised to find that her pussy was swollen and damp, which was the cause of her heat. Some of her pubic hairs had turned a lighter shade of gray-white, and just above her crotch was a tender patch of softer skin.
Only three more hours until Xander gets home...
Mary waited another hour. Her dairy show had ended and now she was watching a documentary about migrating salmon, although she wasn't paying much attention to that. Instead, she found herself focusing on her new changes. Her breasts were definitely larger by at least two cup sizes and noticeably heavier. The nipples had remained fully erect with dribbles of milk leaking out whenever she made sudden movements. She had wrapped a towel around her chest area to keep her nice blanket dry. The rough fibers of the dry towel rubbed against her growing teats, making her more aroused than she had been in a long time. Her nipples were pointy enough now that she could still see and feel their outline through the towel.
Her fingernails had gradually darkened and stiffened until she was equipped with hand-like hooves. She could use her fingers for easy tasks like holding things, but it was becoming increasingly difficult to work the TV remote. Looking in a mirror on the wall to her left, she could see that her nose had grown and widened out into a cow's snout, making her snicker at her ridiculous appearance. Unfortunately, her sense of smell hadn't improved at all, but her ears were long and pointed enough to stick out through her long hair. A whole new world of sound entered through her large ears. She lowered the TV volume by a few notches and could hear the birds outside, someone riding a bicycle outside, and the kitchen sink she left on... oh!
She got up and jogged over to the kitchen. The new jigglyness and sensitivity of her chest and butt sent waves of pleasure to her brain. She had to slow down to a slow walk to stop shaking drops her milk everywhere. She noticed that her tail swung unconsciously from side to side as she walked.
She turned off the faucet and gave one of her teats a tentative squeeze. A tiny spray of milk shot into the sink! Not a lot, but more than would have come out just one hour ago. She went back to the couch and waited a little more.
The tail behind her had lengthened by several inches and was covered in a fine layer of while hairs reaching up to her butt and a little ways up her back. Mary ran her stiff fingers through the small patch of fur and let out a low moan.
The most exciting development in this time was the small udder forming on her lower stomach! A pink fleshy mass had pushed out from Mary's lower abdominal region. It bulged out a couple of inches, stretching her panties a little bit. The intense tingling she could feel told her that it was still growing. Occasionally she would brush a hand/hoof against the sensitive skin to make her entire body to buzz in pleasure.
"Ooooh", Mary mooaned. The way she involuntary lengthened the "O" sound caused her giggle. She had never been so aroused.
Only two more hours until Xander gets home...