You reach the door just as the other you opens it wide, exposing both of you to Sheila's view. At first, she doesn't react, probably astounded by what she sees. Maybe she thinks it's some sort of joke, or make-up. You're not sure, but you know you can't be hanging around the open door, esecially with the other you in nothing but boxers, tail wagging.
Finally realizing something's odd, she gets out a "What the..." before you clap a furred hand over her mouth and pull her inside.
"Close it already!" you hiss at the other you, who obliges, wagging his tail in excitement. You, on the other hand, are not sure how to proceed, but you figure at this point honesty is the best policy. You really like Sheila, perhaps even love her, and you don't want to scare her or lie to her.
"Sorry," you say in response to her widened eyes, "but please, just let me explain first. Can you promise not to yell or freak out if I let go?" She nods slowly, and you drop your hand from her mouth. You lead her over to the couch and sit her down. You lower yourself down on the couch on one side of her, and the other you sits on her other side, both of your tails twitching nervously, much to Sheila's disbelief. You are not sure if she's in shock or she thinks she's going crazy, but you want to try to calm her down as quickly as possible. Trying to make sense out of a nonsensical story, you describe the events of that day in as much detail as possible. Sheila doesn't react much, except for an occasional rasied eyebrow or incredulous look.
"As far as we've been able to puzzle out," you conclude after completing your catalogue of events, "the magic couldn't create a dog me and get rid of the human me at the same time, so eventually it split me into two beings. Maybe the shop itself somehow contributed to completing the split, I'm not sure." The other you nods in agreement. "However, it didn't make a dog me and a human me, but messed up, so I ended up as two me's, both half-dog and half-human. Or at least, we're still becoming half-dog. But I have a theory, after seeing how the other me and I act differently," you continue, much to the interest of the other you. "Maybe instead of both of us having the exact same human halves and dog halves, maybe we each ended up getting different parts of the original me. In other words, neither of us is the original me, only both of us are the original me together. Perhaps its the same with the dog me as well; so we both ended up physically alike, but with different mental and personality attributes."
The other you seems intrigued by this concept, but you're more worried about Sheila. You want her on your side, helping you, but if she can't take that, you at least want her to agree to keep your change a secret until you can find out a way to reverse it. As you gaze at her hopefully, Sheila...