Katie was holding a small, corked bottle full of a clear red liquid. Tied around the neck of the bottle was a paper label with "Drink Me" clearly written on it.
"Hey, Tiff, check this out!"
Tiffany looked at the bottle and laughed. "Someone really liked Alice in Wonderland."
"So...should I drink it?" Katie asked.
"Katie, you don't even know what's in that bottle, and you want to drink it?"
"Come on, it wouldn't be labelled like this if it was harmful. But if you're that nervous, I'll drink it just to show you it's safe."
Katie swollowed the whole bottle. Almost immediately a small aurora developed around her. A lovely blue color. Tiff just pointed at her. Words left her mouth.
"What?" Katie asked. "Why - AH!"
Katie couldn't stop the surprised scream as her ass twitched, jerked, and expanded rapidly rearward. She started to fall forward. Her knees weren't working properly! She caught herself with her hands, but just then two shooting pains from the top of her hipbones made her scream again. She was rising back into the air. Her jeans split and flew apart in an explosion of fabric and her brain freaked out with the sensation of suddenly having three too many limbs!
"Katieeee!"
Tiff was screaming, hand to her mouth. She was backing away!
"Tiff! What's happening to me?" Katie cried. She tried to move forward but the mental confusion was too great. She crossed her forelegs
Forelegs! Oh my GOD!
-and nearly fell. Gasping and shuddering in the aftermath of bone-crushing pain, she braced up hard on all four legs and stood still.
Tiffany was looking up at her with an expression of wonder. Her face was fuzzy in Katie's vision. Katie wondered if she'd broken her glasses. She reached up with her right hand and pulled the glasses off. She shook her (really long, really silky?) hair back with a shake. The instant the glasses came off, her vision cleared and Tiff's face came into focus.
"Katie... the potion. I can't believe it, Katie. You really are a centaur. You're beautiful, Katie..."
Katie closed her eyes. She opened them, and looked down. Her hands came up in surprise and cupped her breasts through the thin cotton of her t-shirt. Her breasts. Not just two little bumps with a nipple in the middle, oh no! Two wonderfully firm and pert breasts! At least a C. Maybe even a D! Katie pawed the floor in surprise and her tail swished in glee.
Tail?
"Tiff?" Katie asked. She absently kneaded her breasts.
"God, we need a mirror, Katie." Tiff said. She slowly stepped towards her friend. Katie realized she was looking down on Tiff from at least a foot of height advantage now.
Tiff walked up to Katie and stopped. Then she surprised Katie by leaning forward and wrapping her arms around Katie's midsection and pressed her face into Katie's breasts in a fierce hug.
Katie stamped nervously and tried to back up a step. Her hind legs weren't cooperating -
"Hind legs."
"What, Katie?"
Katie finally worked up her resolve and twisted her body around. It pivoted at the waist and turned... and kept turning, far past the point where it should have stopped. She felt like - like her whole torso was nothing but one long, lean muscle - incredibly strong and flexible. What she saw caused her to shake again.
Stretched out behind her, beginning at what should have been the base of her spine, was the lean, beautiful body of a horse. It was covered in glossy blue-black hair all the way back to an upraised silky black tail that looked just like the hair on her head. Her... flanks stretched out and down to long slender fine-boned legs ending in sharp flinty hooves.
"I'm a sorrel." Katie said.
Tiff peeked out from around Katie's twisted upper body and looked up.
"What?" She said.
"I'm a sorrel mare. Centaur. Centauress. Whatever." Katie said.
Another shuddering quake ran through her body. She felt a strange sensation from between her hind legs.
Tiff unwrapped her arms and moved to Katie's on side. Her hands stayed pressed against Katie's flanks, gliding across the glossy black coat of her friend's body.
"I guess we do need a mirror. Oh God, Tiff. It worked. I changed. You changed me!"
Tiff had reached Katie's muscular hindquartes. She looked back and up at her friend, still with an awed expression on her face.
"Katie, you're so perfect... I should have guessed. Of course a slender teenage girl wouldn't have a gigantic horse's body. That would look really stupid."
"What do you mean, Tiff?" Katie asked.
"In my books. I always pictured the centaurs as being normal-sized horses with normal-sized human bodies attached, but now I see that would have been way out of proportion."
Tiffany was stroking Katie's tail. It felt really nice.
"You're beautiful, Katie. Your horse half - well, you're pony-sized. No, I take that back. You look like a small Arabian. So fine, so pretty..."
Tiff lifted up Katie's tail and examined her ass. Okay, that was a little strange...
"There's no way a grown man could ever ride you. You're positively dainty."
Tiff looked up and grinned.
"I have the awfulest impulse to go buy a quart of nail polish and paint your hooves." Tiff laughed.
This was all new to Katie. They'd been best friends for almost all their lives, and she had no idea that Tiff was so... obsessed? with centaurs. Sure she knew that Tiff had a crush on her, but centaurs?
Tiff was resting one hand on Katie's butt, idly stroking her ass with a finger. Katie trembled. Horsehide or not, she could definitely feel that!
"Do horses have clits, Katie?"
Tiffany's fingers were - they were - Is that my pussy?
Katie suddenly realized that she was still kneading her new breasts. She pulled her hands back as though burned.
"You ought to take your shirt off, Katie. Centaurs don't wear clothes, and you have beautiful boobs..."
Katie gasped. Tiff had definitely found the heart of her equine femininity. She wanted to pull away. She had to pull away. What was Tiff thinking?
"You know, I saw this on TV once, a show about farm veterinarians. There was this one doctor who was helping a little black mare foal, and the foal was going to be a breech, and the doctor just took his shirt off and - "
"Aiiiih! Tiff - aaann - eeee!" Katie yelped.
The brown-haired girl had just sunk her arm into Katie's centaur pussy up to the elbow.
Through the sudden fog of pleasure, Katie heard Tiff's satisfied chuckle.
"Well, I still don't know if horses have clits, but my beautiful Katie sure does!"