...you noticed Sam had moved away from the tree and was towering above your outstretched body with a look of pure lust in her eyes, a clear liquid dripping from her womanhood.
"No...we can't...," you stutter as you feebly try to move away from her in a vain attempt to overcome the lust. She looked beautiful, her long chestnut hair flowing behind her now slightly larger frame.
"Urgh..." you cry, as in one swift movement she crouches, takes your horse-length dick into her hands and deftly inserts it into the clutches of her tight swollen womanhood. The pleasure was intense as she began to grind against you and as your juices began to mix with hers, the changes continued. She moaned as you both gained more bulk - your upper body barreling with muscle. Your dick felt tighter as you could feel it expanding within her, your balls also expanding and darkening slightly in color. Lost in pleasure, you didn't notice as a nub started to emerge from the bottom of your spine (and hers) - the beginning of a tail. Sam's womanhood also started to take on a slightly darker color as it expanded.
Your feet started to expand and merge into hooves as in one fowl swoop using your newly gained muscle, you hoisted yourself to your feet, still inside Sam as her feet started to change too. From your new standing position, you began to bounce Sam on top of you, as your tails continues to grow. The pleasure and lust kept on increasing to levels you never knew were possible. Had anyone been peering through the bushes, they would have seen what looked like a man and woman entwined in lust, but both with the lower body of a horse. You knew you couldn't hold out much longer as the pleasure reached fever pitch, both of you moaning, having almost completely succummed to the lust. As if in an explosion of pleasure your nose flared as you both orgasmed and you stated pumping copious amounts of thick cum within her.
At this point, you were both exhausted, falling to the ground together in a heap of flesh and juices, your bodies now half horse, half human.