They both gasp and look down. Katie's balls were hidden in a furry brown sack. Short soft hairs, not pubs. And the hair traveling up from her ballsack to her stomach, and around her vagina. Tiffany ran one finger along her friend's scrotum, and Katie moaned in pleasure. Actually she mooed.
"Did you just..."
"I think so." Katie said, blushing. But her embarrassment was mitigated by her arousal. Her clit suddenly felt hot. It was huge, the head the size of a plum. Tiffany took a step back and watched as Katie's clit continued to grow. It swelled, and Katie's hips bucked forward as a rush of testosterone filled her body. Her clit shot out from her body like a rocket.
A slit formed at the top, and a sheath climbed up halfway up her new penis. Black spots began to cover it, until her cock was mottled dark leathery skin. Her balls pulled down, heavy and full. The fur thinned, and the skin became wrinkly and black.
Tiffany's mouth watered, and she continued to stare. She was oblivious to her own changes. Her clit quivered and began to stretch out from her body. Her ovaries began to descend down into her vagina lips. As Katie's own cock stretched to its full 2 foot length, Tiffany's balls fell into place. She moaned in pleasure, and grabbed her friend, bringing her close. The two girls' penises touched and heightened their erections. Tiffany's clit exploded into a full penis.
Katie turned around, her vagina lips now black and swollen, like her anus. Both were coated in girl juices, and smelled like a cow. She pushed her ass up into the air, and accidentally released a load of shit onto the ground. She didn't feel as embarrassed as she should. It felt almost... natural. Her cunt began pulsing as it grew out. Eventually they became so large, they rubbed against her balls.
Tiffany's penis finished its growth into a bull cock, with the head becoming stubby and swollen. It was the size of an apple, and her shaft was as a three feet long. Her balls engorged, dropping down to her knees. She slipped a hand down to tease her vagina, only to find that hers closed up when her balls fell into place. A little upset at the loss of her womanhood, she then catches the scent of her friend's new cow cunt.
Tiffany's penis bobs up and down as she rushes to Katie. Her penis slides inside, and she cries out overwhelmed by the feelings. The two start rutting like animals. They are so lost in their passion they don't realize they've both grown cow tails. The whip back and forth, Katie's hitting Tiffany's nose, which had flattened some.
"You're so tight Katie. Oh my god, you're so fucking tight!" Tiffany screamed, her humping becoming more and more animalistic.
"Further! Fuck me! Take me with that cock!" Kate shouted in response, flinging her ass out. Tiffany's balls slap against Katie's, and Katie reaches a hand down to tug at her breasts.
As she does, her nipples begin to grow. They puff out to five inches thick, and four inches long. And then they start to migrate down to her stomach. Her erect penis rubs against them, and Katie cums. Her bull load is spewed all over the ground, and coats her front. As she ejaculates, her vagina clenches around Tiffany's cock, and then Tiffany cums inside her friend. Katie's cunt greedily sucks up her friend's sperm, and relaxes only after she finishes releasing her own load.
The two collapse on the floor, exhausted. Katie's vaguely aware of her new udder. Two newer, smaller teats have formed under her old ones. And her stomach has bloated and filled with milk. Her udder sloshes around as she rolls over to kiss Tiffany's broad nose. It rubs against her penis, and Katie mooes softly.
Tiffany's bull cock remains in Katie's cunt, the head too sensitive to be pulled out. She butts her head against Katie, and then moves it down to suckle on one of her teats. Each gulp of milk progressing her transformation further. Her face pushes out into a full muzzle, and her ears are pulled sideways. The fur covering her lower body spreads upwards. Her breasts grow to EE size, and her nipples look more like ho-hos. Dark, the skin just as tough and leathery as her penis.
Katie's transformation is brought to a stop as her udder reaches its full size. The size of a basketball, milk leaks out. A wet spot of milk and cum pools under the two. They wrap their arms around each other, and sigh. The two friends, now cow-bull hybrids lovers, fall asleep. The vials left forgotten until tomorrow.