Wild, wild senastions of bestial passion were pumping through Mark's changing mind. His every muscle stiffened with the longing deside to meet the need to procreate as any ture animal might.
Stepping forward he pressed past his human friends and began to quickly make his way to the masion's front door. Ryan and Sei were close behind but even as they ran to stop their friend they wondered just how they could stop him.
"Mark, please don't go out there and do something that might make you impossible to become human again!" cried out Sei.
Mark stopped at the front door and turning his great horse sized head to look over his hairy withers at his friends. Lips spread as he opened his mouth letting loose a harsh and loud whinny of longing desire. Pawing the floor of the mansions foyer he seemed to pause and consider the question.
A long black hairy tail flicked about as if a warning to stay back to the boys. Mark was thinking but not about being human again. Instead his brain was filling with instinctive patterns of equine desire. Lust and the need to procreate was taking its toll on Mark's rational thought process.
Slowly all movement, even his tail stopped and Mark stood in that doorway his head level with the long broad back of his stallion body. Ears forward he blinked his eyes slowly, breathing calmed to a slow pattern of easy breaths in and out.
"That's it Mark think, keep thinking, its the only way you can hold on and not lose your true self to becoming an ordinary horse." begged Ryan as Sei now silent stood by.
Again in a slow and intentioned move mark turned to look over and at his two good friends. Saying nothing, not a snort or whinny did he make. The unfurling of his male horse sized penis, the thing dropped down filling and stiffening to a elongated black shaft.
Turning his head again forward Mark stood there making his giant penis stiffen even more. An urge to make it move had the horse's cock swinging. Mark stiffened his grip on the organ lifting it till it bumped into the rounded portion of his lower belly. A release, and it swung down harshly slapping into his one broadened thigh. Up it came again and the process continued and went faster and with movements Mark began to breath deeply.
"Stop him he's masturbating himself into a real stallion!" yelled Sei knowing from past experience from his time working on nearby farms.
Ryan stepped close to Mark his now equine friend. Reaching his hand up to Mark's withers he tussled the short mane's hairs and asked, "Please , don't go this way, your my friend! Being a horse and this stallion form can't be that much better than being human and a boy?"
By this time Sei and Ryan were joined by Johnny Ryan's younger brother. It was as the two older boys tried to reason with there changed friend that Johnny tried to be cute.