Johnny is saying something about his part of the costume... something about posing for pictures at the party tonight, so Jess nods, distracted with placing the unicorn horn *just so* on her forehead. It wouldn't do to just plop it on and have a fake-looking spiral coming out of the top of her head; she had to get it centered, but low, so that it would look like it's protruding from her forehead, like a "real" unicorn... she chuckled to herself at the pun, absentmindedly answering her oh-so-tolerant, easy-going boyfriend at the same time:
"Of course. Just for pictures." she murmurs, fluffing her hair to better hide the clear, plastic band. “Here, put the wings on! We might as well see if they fit and look good, then we can choose what version we want to go as.”
He takes the wings and she can see that he is pulling them on in her periphery, but her reflection distracts her once more: the horn must have been coated in some loosely-applied glitter... suddenly she's shimmering all over, the flecks seeming to spread outward from the unicorn horn, fluttering down her face to dust her collarbone and shoulders. Jess leans into the mirror, brushing her hands over her chest in an effort to dislodge the loose glitter, but it just seems to spread further, coating her fingers and somehow her arms... it's even all over her ribs and stomach - there must have been more glitter in the fur of the costume? Whoever rented this set last seemed to have gone a LITTLE overboard on the "sparkly unicorn" theme!
Absorbed with the "glitter issue," knowing that despite his laid-back demeanor, Johnny definitely had a breaking point when it came to costume tolerance, and that being covered in old, "used" glitter most likely crossed that line, Jess completely failed to notice the changes occurring TO her form, much less those occurring to her boyfriend.
Briskly brushing her hands down her arms, Jess didn't realize that her posterior was swelling, her spine elongating as it pushed backward, pulled down by gravity but growing and expanding rapidly at the same time. Nerve endings completely numb, or ... disconnected, she didn't feel a new ribcage forming behind her, filling the costume's hole that they'd assume was meant for her partner. Nor did she feel the two nubs that rapidly grew into limbs, bulking up in an instant with fur-covered muscle to match her forelegs even as they formed hardened hooves and touched down on the dressing room floor. An entirely new part of her body had sprouted, grown and formed supporting limbs before Jess could even notice a shift in balance!
It was the tail that finally caught her attention.
A tassel of hair, unconsciously flicking with the agitation of new growth, rapidly sprouted from the new base of Jessica's elongated spine, brushing against her furry thighs and flashing into view in the changing room mirror. Despite the visual proof, her brain literally *could not* process what it was seeing, and instead her eyes were drawn down to the plight of her boyfriend, who Jess suddenly noticed was crumpling to the floor!