It seemed to be getting harder in her hand, swelling more. His cockhead, she decided, had definitely become larger. His piss hole was starting to flare open, and juice dripped more than before. In fact, the juices bubbled from his piss hole and ran down to her fingers, making her fist slippery. She noticed that his balls were no longer loose, but were getting tight. She watched them with youthful fascination as they drew up against the base of his cock.

She became more excited by his balls than by fingerfucking her pussy. Pulling her finger out, she stretched her hand into the back seat. Sharon cupped his balls, feeling how hot they were, too. She kept jacking up and down, unaware that her fist was getting tighter and tighter on his cock. She began to gasp and pant, her lovely body trembling. She knew something was about to happen, something she had only heard about at school during those secret, hurtfull talks among girls.

Sharon wanted to see it happen.

Throwing caution away, she gripped her brother's cock as hard as she could, puffing and pushing on it. She held his balls tightly, soft mews coming from her as she gazed at the swollen prickhead. She felt his cock throbbing with more power, and he was writhing his hips.

Suddenly, a thick gush of come juice spurted from his piss hole, flying a good foot and a half into the air. Jimmy groaned in his sleep. If he had woken up then, Sharon could not have stopped herself, she was so absorbed in this strange thing she was seeing. The stories she had heard about boys were true after all.

More squirting comejuice boiled high from his cock, splashing back down on his shorts and her fist. Sharon couldn't swallow the squeal of excitement she felt. She gripped his cock, her fist pumping in a frenzy, seeing if she could keep him spurting that way. His balls in her hand seemed to writhe as he shot his thick come juice high into the air.

"What's going on?" Jimmy woke up, his cock gushing, his sister's hand jacking him frantically. "Sharon! What are you doing?"