Suddenly, there was a loud "Ho-ahhh!" and a Squeak! Squeak! of rubber on concrete. Mark started and turned, to be confronted by one of the most physically imposing female specimens he'd ever seen.
The blonde pony leaned slightly forward with back arched, to balance the weight of the rider on her back, but even in that posture she matched Mark's 6-foot height. An explosive exhalation from the startled creature's capacious lungs escaped her gaping mouth and spattered Mark with droplets of spittle.
"I say, old boy," said her rider, who now wrestled to control his spooked mount. He sat upon a small saddle strapped to the pony's lower back, his legs projecting out and forward to keep clear of her high-stepping knees. His hands grasped a curved handlebar, like that of a bicycle, that projected from either side of a short hollow cylinder strapped end-first into her mouth. Within the cylinder the pony's red tongue wagged. Now the rider used the handlebars to wrench the big, blonde head to the left, to stop his mount's sudden and undesired pirouette to the right. Her full, pink-tipped breasts bounced crazily between the straps of her black harness as she danced jerkily, out of control.
Finally she settled, stamped her feet twice and stood, her broad chest heaving. From cheek to shapely legs (if young oaks can be shapely), every inch of skin not covered by harness or boot shone with the sweat of her exertions.
"You must take more care crossing the track," the rider scolded. He was a neat middle-aged gentleman of medium height and build, moustached and tweed-jacketed. By his accent he'd just flown in from across the Pond. "Blinkered as she is, Violet might have trampled you, and all of us come to grief."
"Sorry," Mark muttered as he wiped specks of pony-froth from his face with a handkerchief. Looking again at the erotic steed's tack he grasped the meaning of "blinkered". What he'd taken at first glance for a blindfold was really a very low leather visor, that allowed her to see only the ground a step or two before her. Mark's glance fell to her feet, looking for the tall heels that he expected whenever he stood eye-to-eye with a female. But her shiny leather boots were nearly flat and rubber-soled, with round toes and a proper arch. This was no show-pony, but a high-performance riding model. Fully erect and unshod, she would have stood a few inches over 6 feet.
The crisis now passed, Violet's rider could not suppress a grin at the obvious impression his mount had made on Mark. "Right, then," he said, and twisted the right grip of his handlebar. The pony bucked slightly as a Snap!Snap!Snap! was heard, and began to accelerate down the track. Beneath the saddle Mark glimpsed little blue-white sparks emitted by the electric "whip" that now caressed her muscular buttocks. As she worked up to speed and settled into a pace to match the whip's rate, the sparking stopped, and Mark understood how such a large creature had managed to surprise him.
At stride she moved silently, her wide hips swinging to absorb the motion of her legs while her upper body and rider glided along quietly. The hip motion was much more pronounced than in a typical jogging female, since Violet did not have any arms to swing. Mark resolved to get a better look at the pony and her tack at the paddock, and thought he might suggest to her master that she be belled, for safety.