You take the equine phallus out of its bag and place it on the common room table, placing it on its flat bottom so it arcs up and back. Your stomach growls, reminding you that you ate very little during your weekend on the island, trying to avoid anything that would cause unwanted changes. You leave the room, ready to go get a meal.
Unfortunately, the dildo isn't just a simple sex toy. It is a piece of Pleasure Island, and as such harbors a sliver of the island's transformative power. And since the island has tremendous power, even a shard of that is still potent. While you were away, your roommate, Jack, entered the room. You didn't know that Jack had certain fetishes, or that he would try to simulate oral with the dildo. Jack took it into his room, locked the door, and slid the shaft down his throat. He thought he could wash it off afterward, hide what he had done. He did not expect the dildo to actually cum down his throat, and cause him to swallow all of it. He also did not expect for the entire phallus to turn into semen and slide down his throat. And he certainly did not expect his penis to lengthen into a horse cock, his balls to swell, or his feet to turn into hooves. Jack's muscles grew, ripping apart his clothes, even as dark brown fur sprouted over his body and a tail extended from his lower back. By the time he overcame the shock of swallowing horse cum, his face had already changed into a more equine shape. Jack, your roommate, had become a horse-man.
And while you were out getting pizza, you weren't thinking about the consequences of bringing a dildo back from that accursed island. You didn't know that your other roommate, Greg, had returned to the room while Jack was finishing his change. You weren't aware that Jack burst out of his room, mind overcome with lust, and forced himself on Greg. Jack used his new strength to rip off Greg's clothes and hold him down, all in one move. Nor were you aware that Jack had forced his new horse cock into Greg's anus, thrusting until the horse-man was pumping his seed into the poor human. Jack was still holding on to Greg, feeling how his partner was growing fur, changing into an equine shape. Greg was dimly aware of what was happening, but it was slowly being overcome with lust.
You ate your dinner, unaware of the plague you had just unleashed.