He swings open the door and sees you standing in front of the mirror partially dog and really wet.
"It's not what it looks like!!!" You exclame.
"Oh my god" he says "what happened to you".
You tell him everything, excluding the part about you getting wet from the thought of him.
"Why is your underwear soaked?" He asked
You blush and look down, embarrassed by your thoughts. "I- don't worry about it" you blurt out.
"How are you going to hide this from Mom and dad?" He asked.
"I don't know, can you help me?"
"Uh, yeah I'll see what I can do. Come on."
You follow him to his bedroom tail between your legs, literally, and he pulls out a pair of loose boxers and some baggy jeans. "Here you go" he said. "This should hide your tail".
"Thanks" you say as you pull off your shirt and underwear pussy still wet.
You notice that you brother hasn't left the room or turned around. He's just stood there staring in shock that his sister was stripping in front of him. You turn away from him and bend over to pick up his boxers lifting your tail up revealing your soaping wet sex to him.
"Uh, sis?" Your brother says
"Yes?" You look back at him, making sure to keep your pussy in front of him.
"Are you in heat?" He asked curiously
You see that he has a hardon and it's definitely bigger than eight inches. "Why do you ask?" You ask playfully.
"Because I think the pheromones are getting to me" he says collapsing to his knees "I can't help myself anymore". Just then he grabs your ass and pulls it close enough to lick your sex. You feel his tongue get longer and his nose push into your sex. He was growing a mussel. You can feel every one of his taste buds change and reshape on your sex. It feels better than anything you've ever felt. You let out a whine of pleasure and look back to see him jacking off a ten inch dog penis in one hand and holding your ass in place with the other. At that sight you cum hard in his mouth. You roll over and see that his ears have turned into German shepherds and slid up his head while his mussel has grown some hair. Also you have two new pairs of tits and your pussy has become more dog like and is covered in fur.
Your brother is licking the cum off his lips, eyes shut while jacking off his cock. You have condemned your brother to the same fate as you.
"Oh my god" you exclame slapping your brothers hands away from his cock "look at us, we're turning into dogs, we have to stop now!!"
You stare at your brother, now half dog, "we need to stop before we end up as dogs".