Her vagina

Without warning, she landed onto his young and erected cock, making both of them moan hard.

"Are you guys okay? That was a nasty bump and I heard noise." His mother said, completely unaware he was fully inside of her sister.

"We are fine, mom! Just fine!" He said, gripping onto his aunt's thighs, holding her down onto him. She tried squirming off of him, but he whispered in her ear.

"If we make too much noise, she will notice, if you lift off me right now, another bump might just slam you right back down. We have to stay like this for a bit longer until we get on a less bumpy road."

His aunt nodded, and tried not moving her wide hips too much. They would have to sit this one through.

It didn't help matters as more bumps came, making Terry shake onto of him, and he tried his best not to thrust harder into his young aunt.