Tiff, not paying attention anymore to her friend, began using her arm to bring Katie pleasure. She even had gone so far that she was even licking Katie's horse pussy.
Katie, meanwhile, was feeling pleasure not only from her rear, but her face too. However, when she looked up, she was shocked at what she saw. Her breast had melded into a solid piece of flesh and were rising up to meet her face. She was about to screem to get Tiff's attention, but the combination of her face stretching, and her breast flesh over her voice box seemed to mute her completely. Not that it would have mattered anyways, as at this point Tiff was so lost in pleasuring Katie, that she forgot the world around her.
Katie then watched as the extra flesh meet with her face and stretched everything out alot. But, even with everything changing on her face, Katie was still able to keep her eyes open, and continued to watch her changes.
Next was the top of her head. Her ears, which had relocated themselves there, became pointed, and were covered in fur the same color as her hair. And as for her hair, it seemed to receed off the side of her head, leaving brown fur were it used to be. Finally, Katie's hair formed a mane between her ears, and it ran down her neck and back.
While she had been watching this, she hadn't noticed that she had lost feeling in both of her arms. However, what she did notice was that her arms were shrinking into her body, and the fur from her lower half was now racing up to meet her face.
Her face, now even more changed, greatly resembled that of a true horse. Her whole jaw was pushed out into a muzzel, and her teeth had become large and flat. It was then that the fur raced across her face, and that the rest of her head completed it's reshaping. Also, what was left of her human body quickly became her new neck.
Katie was now staring at a pony. And even now, she felt her body begin to grow. Little by little, she grew to the size of a normal Arabian. Meanwhile Tiff, who was oblivious to Katie's changes, was still working away, not noticing that she was now pleasuring a complete horse. And it wasn't like Katie was going to stop her. Between her latest transformaion, and her friend still pleasuring her, she could do nothing, not even make a noise.
However, this would all change as Katie finally began to feel the building of an orgasm. Tiff was now using her whole arm, and was licking wildly at Katie's pussy. No longer being able to stand it, Katie finally let herself go in one great explotion of horse juice and pleasure. Tiff finally noticed something, when she heard a horses niehing, instead of her friends moans. So Tiff looked up.