You figure a tail will complete your look; after all, most fantasy dog-person artwork you've seen includes a tail, right? People will just think you enjoy cosplay. But how do you grow just a tail without changing any other part of you?
You come to the conclusion that the method that worked on your ears should work for a tail as well, although you are not sure, since a tail would involve creating an appendage that did not exist in the first place. Nevertheless, you boldly continue. You rummage through your closet for an old pair of pants, and after some alterations, swap them for your current pair. You gird yourself again in all your protective gear, although this time you have to cut new holes in the ski mask for your ears, which twitch in excitement. You have to remind yourself that you're not doing this for fun; after all, you could be stuck this way for a very long time. That thought sobers you up a bit, as evinced by a slight droop in your ears. Still, you are curious about the idea of having a tail, and if having dog nose and ears are any indicator, you will be in for some extraoridnarily new sensations.
Again taking a deep breath, and almost grinning under your face mask at the awkwardness of the situation, you reach around yourself to spray the small hole you cut in the old pants you are now wearing, located at the base of your spine. After giving it a generous spritz, you quickly put down the bottle of BOD and run to the mirror. You take off the masks and glasses, and hurriedly strip off the pants as you feel a strange tingle from your rear. This time you want to see exactly what happens.
You are aware of the now-familiar itch beginning, but this time you actually see your body begin to reform itself. A tiny nub sprouts from below your waistline as it feels almost like your spine is lengthening at the bottom. You barely have time to hope that you won't end up with a short stubby tail before the change takes on new proportions. Although to your eye it looks like someone is stretching your skin like a rubber band, your brain is somehow processing the fact that new bones, muscles, and nerves are being added just as quickly as the skin is expanding. Even before the change is complete your naked tail can move slightly in response to your concentration.
The itch has not ended, however, but rather becomes more intense. Almost like watching a high-speed film, you see fur sprout from your nearly three-foot-long tail. The color matches the fur which grew when you sprayed yourself earlier, and lengthens enough that it sways as your tail wags.
YOUR TAIL! you think to yourself almost giddily. You again want to scratch, as you did with your ears. You twist around and grasp your new appendage, almost jumping when you feel your hands through the new nerves in your tail. You scratch a bit, but you are wary of tangling the fur. You pick up a brush from the countertop and gently use that instead.
You can't think of words to describe it, but the feeling of brushing your tail is definitely pleasurable. Your tail slips from your hands and begins to wag happily back and forth as if to accentuate the fact, and your ears and even nose twitch in joy. You examine yourself in the mirror, surprised how well you've adapted to this new canine appearance. You are even tempted to go further, but you know that it is an irrational desire. Even going this far has put yourself in serious danger of being carted off to a lab somewhere if you are discovered.
Pulling yourself back to reality, you decide you have to test your new appearance somewhere where it wouldn't stand out too much, just to see if it will pass as a costume. After customizing a pair of underwear and pants with a hole big enough for your tail to fit through, you finally manage to thread the appendage through your outfit, despite the apparent fondness for wagging. In order to complete the illusion that the dog parts are a costume, you grab a small headband and put it immediately in front of your ears, hopefully masking the fact that the ears are attached to your head. Your hair should cover for the lack of human ears. You think ahead enough to place a small random electronics box in your rear pocket, hoping that you can claim to have a battery-operated animatronic tail should your tail move involuntarily, as it seems wont to do. You even faintly draw a few whiskers on your face to draw attention away from your too-realistic nose. Satisfied with your reflection, you head downstairs to decide on a location. After some thought, you decide to go to...