Cal picked up his much smaller older sister and threw her on the bed.
"OK, sis, I'll make you my bitch, but first I'm gonna show you who the big dog is around here," he said as he unsnapped the colalr from Katy's neck and clicked it on to his own. "Now take it like a dog, you cunt," he said as he flipped her over and quickly drove his penis into her dripping pussy.
As her brother shoved his cock further and further into her she longed to have it back around her neck, though she still felt its magic working on her as images of dogs having sex flooded her mind.
Suddenly the feeling of her brother's penis began to change... the tip became more bulbous, and she felt more hair on his legs and stomach. His hands, which had been resting on her shoulders, suddenly got smaller and sprouted sharp claws. She could hear him shouting...
"What the fuck is happeni...oooooooooooooooooooooooooooh" Her brother's voice was transformed into a scared howl. She looked out of the corner of her eye and saw in the mirror that Cal had become a huge German SHepherd, and that he was driving his dog cock into her pussy.
Katy arched her ass more to make it easier for Cal the dog to enter her fully as he pumped away at her. With a loud yelp he ejaculated inside her, her pussy gleaming wet with more dog cum.
He slumped off of her and padded around in a circle. She stood up and looked down at him, deciding what to do next.