You furrow your brow in thought. A dog you, with all your memories and intelligence, is an interesting concept...as long as you're not the dog.
"But if you're the dog," you ask the other you, "then why do I have a dog nose still? I mean, wouldn't you be more dog than me, and I'd be more human? Or vice versa?"
"Hmm, I'm not sure," the other you ponders, scratching his head. This action draws your attention, when you notice something rather odd taking place. As the other you scratches, his ears seem to enlongate a bit and travel higher up on his head. By the time you point at him in disbelief, his pointed ears are perched proudly atop his head.
"Well, I guess that means you are more dog than I am," you state, indicating his ears.
"I wouldn't be so sure," the other you replies, gesturing at your own head. Clapping your hands to your head in dread, you find your own ears are now quite a bit higher than they used to be, and rather triangular and furry. They twitch involuntarily as you run your fingertips over them in shock.
Your counterpart, who seems to be reacting to this mutation better than you, is still mulling over your question.
"The only possibility I can think of," he finally says, "is that something went haywire, and instead of me being all dog and you being all human, or the other way around, we ended up with two forms, and maybe we're both half human and half dog."
"But we're not half dog..." you cry out worriedly.
"...yet," the other you responds, and reaches behind him to adjust his pants. You notice a strange motion behind him.
"Is that your...." you can't bring yourself to say it.
"...tail," the other you states happily, as the new appendage wags back and forth. You reach for your own backside in horror, and realize you've been having a strange sensation of discomfort for a while. You pull down the back of your pants and boxers slightly, and to your dismay, out pops a rapidly-expanding tail of your own. It itches a bit, then begins sprouting fur as well. You can't believe this is happening, and you are slightly annoyed that your other self seems to be enjoying it so much. You don't want to be half-dog, or any-dog for that matter. You desperately begin to...