"Oh, Jesus!"

It was true that as children they had played doctor and nurse regularly. Now as Billy gazed at his younger sister he felt confused.

In a way he wanted her to look at his cock and admire him. On the other hand he knew it was wrong because his parents had instilled certain values in all their children.

Penny clutched the towel and openly stared at the naked boy. "Your cock got real big," she said, her eyes shining with admiration.

"Mom'll kill you if she finds out you're doing this," he said, suppressing a grin.

"Hey, it's lifting up," Penny said.

The boy felt a twitch in his balls. Damn it, he was getting turned on and by his own kid sister.

"Jesus, you better get out of here," he said.

The little brunette let the wet towel drop to the floor. When Billy didn't reach for it, she moved closer. "I like looking at your thing. It's sort of cute."

"Jesus, cute!" he groaned.

She moved closer, without thinking, reaching for his prick. "I don't mean cute," she said. "I mean horny and masculine."

"Hey, cut that out!" He moved back, hitting the wall. "Jesus, Sis, you can't do that."

"Just let me touch it a minute," she said.

"You're crazy," he said, but he stood still while she touched his cock.

He had noticed in recent years that his sister was growing into a very pretty young lady. She was built too. She had big tits like their mother and a nice round ass. He had wet dreams about her sometimes, but it had never occurred to him that she was horny too.

"It feels funny, but it's nice," she whispered, lightly running her fingers over his fuckpole.

As she spoke she stepped back and gazed down at the prize in her hand. The boy stared at her dumbly. He and Jimmy talked about cooze all the time, but they'd had little experience with sex. Now here was Penny, his own sister, squeezing his prick. His confusion increased. It felt good, but he knew he ought to make her stop.