Before diving into the box of body parts, Dylan noticed a sheet of paper tucked into one side. Scanning it, it was a disclaimer and guarantee. "As part of our commitment to safe morphogenic exploration, all our products have strict anti-feral protections. The one who wears these parts will always be left in a position to remove them without external assistance, and morphological limitations guarantee hands will retain enough flexibility in fingers and opposable thumbs to maintain humanesque mobility or double your money back!" Amused and a little reassured that there seemed to be safety in this, he plunged his hand into the box.
Rummaging past the feeling of smooth scales and fluffy fur, trying to decide what to "wear", Dylan's hand encountered a new sensation, that of leather. Curious, he grabbed and pulled it out of the box. He was holding a grey wrinkled rope, maybe a foot and a half long, with a smooth circular base on one end and a darker brush of hair on the other. Like all the other appendages in the box it looked rather inert, even harmless, but instincts humans seldom needed told him that was not the case.
"An... elephant? Okay. Go big or go home, they say..."
The problem was how to put it on. There was no belt or strap to hold it in place. There wasn't a clip or a pin to attach it to his clothes. He might have been able to tuck it into the back of his pants, but then it could be dislodged with little effort. The smooth circle that comprised one end gave no obvious clue what to do. Leaving the tail on his bed, he slipped into his parent's room and searched his mother's sewing kit for a couple of pins. He didn't look forward to having to pin the thing behind him alone, but it wasn't like he could ask his parents to help. However he didn't even get that far. He tried to thread one of them through the base, but it wouldn't pierce the leathery skin of the tail no matter how hard he pushed. Confused, Dylan pricked his finger with the pin, and winced at the jabbing pain while a bead of blood appeared.
"I didn't think elephant skin was THAT tough," he said, grabbing the tail with his pricked hand and walking to the mirror on his wardrobe door. "Maybe I should try and get an idea of where I'd want to attach it before I try ag- egh?!"
As he had gotten in position looking behind him, maneuvering the tail below his belt, it had suddenly squirmed in his hand, leaping forward towards the seat of his pants. He only felt its pressure against him for a split second before an electric arc shot down his spine and his entire lower back was smothered in warmth. As a reflex he bent forward, hands retreating from the area to clutch his knees and keep himself from falling forward. The warmth did not get any hotter, but it felt more intense, or at least that's how Dylan's brain could describe it. There was no pain, it wasn't unpleasant in any way, but it was a feeling he had no frame of reference for. And just when it threatened to become uncomfortable, it stopped.
Dylan stayed in his semi-crouched position, taking unusually deep breaths, uncertain of what to do next. Part of him completely understood what had to have happened, regardless of how impossible that was supposed to be, but his higher functions made an admirable effort of trying to deny it. The sensation that the base of his spine felt exposed to the air finally demanded he investigate. Not quite ready to look, one hand left its knee and slipped under the back of his shirt. Smooth skin, just as normal. Descend. Still smooth. So far so good. Leaving the shirt now, under the belt. Still smooth- wait. His spine somehow twitched as the normal arc of his back made an abrupt turn outwards, the smooth skin suddenly becoming wrinkled leather.
This was enough for him to look behind once more. The tail had leapt through his pants, tearing a hole on its way, and now stood slightly raised, not limping as a prop might have. Seeing the appendage helped his brain contextualise the strange sensations his spine was reporting, and the strangeness melted away as a result.
"This is... This is so cool!"
He'd meant to say it was weird, or scary, but an optimistic impulse overrode his sensation of the odd. Still looking behind him, he tried to command the tail to move. It twitched, swinging left and right as it swatted his legs or his back, but he found it extremely hard to keep it in a position other than straight behind him. It wasn't like the tail of a monkey or a cat, with the dexterity to act as an auxiliary limb. But this shortcoming was ignored in favour of this situation's mere existence. Letting giddy chuckles escape his mouth, Dylan grabbed his tail, tugged it slightly to confirm it very much was part of him now, and brought the brushy end in front of him to expect it. He wasn't sure whether it naturally felt good to touch his tail like this, or whether it was the novelty, but he inspected the wrinkly rope as best as he could. The brush of hair looked larger, and it had changed from a dull grey to his brown hair colour. Also the fact he could bring the tip almost up to his shoulder suggested the act of fusing with him had caused the tail to grow, maybe another six inches or a full foot, or possibly even more. He decided this made sense, as some of the tails looked like they belonged to dinosaurs or crocodiles but were barely the length of the box. Maybe this was a more appropriate human size.
Enraptured in this moment, Dylan found himself at a loss about what to do. He thought of taking a picture, but decided everyone would think it an edit. Invite someone round to show off? That was more appealing. But a selfish thought stopped him. He'd have to share if he revealed this to everyone just yet. He'd rather get a feel for how this all worked, maybe look in the box for actual instructions, so he could maximize an audience's amazement. But he didn't feel like learning anything just yet. He wanted to wallow in this moment of having a tail. The tail rewarded his decision by swinging back and forth in response to his elation, a lethargic imitation of a dog's tail wagging.
Deciding to practice something basic, he sad down at his desk, carefully threading the tail through the gap in the back, and began to read a book, letting his subconscious swish it wherever it wanted. His deep breathing had steadied to something more regular, but it had inflicted consequences on him he hadn't realised. He was so caught up in the sensations of his elephant's tail that he completely missed his shirt was slightly tighter on him. The tail had grown, but would it be the only thing changing size? And was it finished?