You blinked in surprise when you saw that the mare wasn't a normal horse, in fact she had a horn sticking out of her forehead. I blinked and looked back towards the attendant but she was busy with something. When you turned back around you saw that the stall had strangely opened up without you noticing.
"Well, you're a curious mare," you said as you downed the rest of the water and moved into the stall to get a closer look at the strange mare. You barely noticed as you felt an itch which you ignored as you moved in closer as a strange scent hit your nose that made you feel a bit aroused strangely enough.
You put your hand on the mare's muzzle as she turned her head and looked at you with a sad look on her face. Out of curiosity you touched her horn as if to see if it was real, it was definitely real and attached to the Unicorn's (since that was most definitely what it was) head, even if it confused you a little.
You felt your arousal growing as a tent formed in your pants. You moved back behind the Unicorn and she pushed her tail to the side as her vagina winked at you and the smell got even stronger, meaning she was probably in heat.
As your fingers started to feel stiff you pulled off your clothes as your cock looked larger. As the itching feeling started to spread you didn't notice, instead you were more focused on mounting the mare in front of you. She looked back at you and let out a whinny as you placed your hands on her flanks and prepared to penetrate her.
You paused a moment as something was pressing at your mind. Your instincts were telling you to mate with her, but somehow you weren't sure if you really wanted to.