Cal sat on his bed and looked at the collar. He put it on and felt the transformation begin... hair sprouting, his cock becoming bulbous. He slipped it off again and everything returned to normal.
He liked being a dog, and had been much more excited about fucking his sister in her dog form than he could have imagined. But he had another idea. If it worked...
He climbed out the window, across the garage roof and dropped down, the dildo and collar in his backpack. In a few minutes he was at his friend Mark's house.
He let himself in. Mark was on the couch playing his X-Box and didn't even look up.
"Dude," Cal asked, "can I borrow ginger for a while?"
"Sure, dude." Mark shot back without questions, his eyes still fixed on the screen.
Cal went to the front room and saw Ginger lying there. She was a purebred Irish Setter, about three years old. She stood up as Cal entered, sniffed his hand, and licked it. His cock throbbed slightly as he thought what he had in store. He prayed to himself that his guess was right.
He put Ginger's lead on her and led her away. Soon they were in the clearing in the woods where Cal and his friends smoked pot. Secluded and secret, just right.
He took Ginger's collar off and slid KAty's on to the dog's neck. She looked up at him with an empty stare. He took out the dildo and slid it into the dog's vagina. She yelped slightly as the bulbous head pentrated her, then relaxed as he pulled it in and out of her. She seemed neither excited nor hurt by his actions.
Soon however, she began to get a scared look in her eye, and whimpered softly. A smile lit up Cal's face as he watched the dog elongate, the hair on her back and legs receding to reveal creamy pink flesh. Her nipples disappeared from her now hairless torso and a perfect round youthful set of human breasts sprouted from her flattening chest. The hair on her head, on the other hand, sprouted out thicker and longer. Her face too became suddenly human.
Cal took a step back in near disbelief. In front of him, kneeling on her hands and knees in the dirt of the clearing, was a gorgeous redheaded woman of about 20 years. Her flowing red hair covered most of the thick leather collar around her neck, but her naked body was clearly well formed and athletic. She looked up at Cal and whimpered.
He put out his hand as he approached her and she sniffed it absently. She looked up at him with a blank expression in her eyes and licked his hand with her very human tongue.
"My God," Cal thought. "I have a hot woman with the mind of a dog." The possibilities reeled out of his mind faster than he could process them.