Erika awkwardly followed Melissa and her sister, Vanessa, to the car. She sat in the backseat quietly, trying to look as innocent as she could... but tucked under her waistband, her erection was buzzing along her heartbeat and would not go away.
"So, what's up sis? Still feeling sick?" Vanessa asked after she had removed her leather jacket. The car radio turned on when the car started, and Erika had to focus a little to hear the conversation between Melissa, on the front seat, and her sister.
"Yeah, that's right..." Melissa replied a little absent-mindedly. "Erika probably caught that stomach bug too." It was impossible to see the expression on her face from behind.
"Uh, yeah I suppose so!" Erika said a little too cheerfully, her voice cracking on the last vowel. "You can just drop me when you reach your place, and I'll walk the rest of the way home, it's fine."
"Sounds more like a sore throat to me, but alright", Vanessa joked. "Oh, I love this song!" she changed subject, turning up the music volume. It was some metal band Erika didn't know.
Erika squirmed uncomfortably on her seat, holding her school bag on her knees. Behind it, her raging hard-on was starting to creep up the confines of her small panties. As she pressed her palm on the bulge of her skirt to push it down, her balls churned and blasted a gush of pre through her thickening member. It throbbed blissfully.
A dark stain spread on the front of her skirt and waistband, near her right hip. Meanwhile, the two sisters on the front of the car were still chatting together, oblivious to Erika's condition.
Erika took an inspiration, trying to keep her breath under control. Tugging on discreetly on her waistband to see the damage, she looked down on her growing penis. A glistening head emerged, fluids dripping from the tip. Erika wiped the glans with her thumb, causing her member to stir and expand further as the skin pulled back.
Mesmerized, Erika watched helpless as her erection extended in the open and upwards, growing both in length and girth. Between her legs, her expanding balls were hurting from the lack of space to fill. As the moist skin of her beast was turning a dark shade of red, the mushroom head of her penis became pointier.
Pushing down on her mutating penis with both hands to keep it out of sight, Erika repressed a lewd whimper. She wouldn't be able to get out of the car without drawing attention to her "little" problem in this condition. On this thought, her cock throbbed harder under her hands, and a new surge of pre oozed out and dribbled down.
She was so ashamed, but it felt so good! She tried to adjust her grasp on her slippery monster cock, but she could barely keep it down. Now the base of her canine penis was swelling again, and a fat knot pushed past the waistband, resting on her laps.
As a piercing guitar solo was blasting through the car speakers, Erika lost control of her cock and bucked her hips once, blasting canine seed in the air!