You get on your knees, now at his level you say "we have to stop".
He said nothing and got to his feet. You start to get up too but he puts his hand on your head and pushes you back down "hey, what the he-" he cuts you off by shoving his 10 inch cock down your throat. "Sit bitch!!" he said. He managed to fit about half of it in your mouth.
"That's right bitch, take everything your little mouth can" he said with a devilish smile. Without any warning he came down your threat and you were forced to swallow. He pulled his dog cock out of your throat. As you gasped for air he pulled you up and bended you over his bed. He spread your ass cheeks and pressed his monster of a dick aginst your ass hole.
"Please, no, no don't do it please" you plead tears running down your face now mostly dog as your hair falls out.
You don't notice that your brother is now covered in fur. His tail wagging uncontrollably.
He slowly slides his dick into your ass hole and puts his hands on your wrists as your back pops into the place of a dogs. He slowly slides in and out as his back pops into place and his hands turn into paws.