You sift through a pile of costume pieces, noting the remarkably realistic nature of the pig's nose, the rabbit ears, and so on. Nothing strikes your fancy until you come across something particularly soft. Pulling it out, at first you think it's a piece of fur. It's only when you hold it up that you realize it's a tail - a wolf's tail.
Inspecting it closer, you see it has a stud-like pin on one end for it to attach to clothing. It seems incredible accurate, and you swear you can feel a skeletal structure of the tail underneath the fur. It's not like you were really planning to buy anything, but you can't help but be amused. Finally, you decide to purchase the wolf's tail. While you are slightly embarrassed about paying for such an odd item, the cashier can't care less, and seems like a bored high-school temp worker. You quickly grab your receipt and leave the store.
After finishing a few errands, you arrive at home. While putting away other purchases, you come across the tail, which you had almost forgotten about. You can't help but stroke it, reveling in its softness, and since there is no one to see you, you decide to wear it and see how it looks. Heading to your bedroom, you drop your pants and carefully stick the rather thick but sharp pin through the seat of your jeans, placing the pin back over the sharp end. Pulling your pants up, you walk over to the full-length mirror and admire your handiwork. You have to admit, it looks pretty cute, like it was made for you. That's when you feel a sudden, sharp pain from your backside.
"Aah!" you cry out involuntarily, taking a half-step forward. You wonder if the pin back fell off when you pulled up your pants, and now the pin has stuck you. You reach down and tug on the tail, which seems to be stuck, and your rear is starting to hurt now. Gritting your teeth, you grab the tail with both hands and pull.
"Yeeowwwch!!" you screech, tears coming to your eyes. You let go of the tail and pant, nearly doubled over in pain. But there was something strange about the pain. And the tail. When you let go, it almost felt like it...moved? But that's impossible, right?
Steeling yourself, you unbutton and unzip your jeans, and grabbing your underwear as well, gently pull it down. Much to your horror, when you look at the pants where the tail should have been pinned, there is a rather large hole, which matches up with the hole in your underwear. Stunned you turn slightly and look in the mirror. Sprouting from the end of your tailbone is the wolf's tail, as though you had been born with it.