Kathy became hot as she watched Cindy's cunt being penetrated by her brother's finger! She could see the lips clinging to him as he finger fucked her, and she knew Cindy had a tight twat. As Robert finger fucked his sister and Cindy jacked on his cock, they talked about Kathy as if she weren't sitting there with them.

"I bet Kathy's cunt is about to come again," Robert said. "I bet she has a cunt as hot as yours, Cindy."

"Sure she does, silly," Cindy giggled. "You can tell because her nipples are hard."

Kathy's nipples were hard, all right. They were very hard and tingling and she wanted to touch them. But she was tied up. Her cunt, too, wanted to be touched, fondled, played with. Her pussy was twitching wildly again and she knew that if they kept this erotic play up she would come again.

"Wanna fuck?" Robert asked.

Kathy jerked her eyes from his finger sliding in and out of Cindy's cunt, thinking he was asking her if she wanted to fuck. But he was talking to his sister.

"Do you wanna fuck me, Robert?" Cindy teased.

"I'm hot as hell to fuck," Robert replied, pulling his finger from her grasping twat. "Come on, Cindy, let's fuck!"

He's going to do it, Kathy thought wildly. He's really going to fuck his sister! Oh, what am I going to do? Should I tell their parents when they get home? They'll have to untie me before then, surely.

Giggling in a lewd sound, Cindy sprawled back on the couch, spreading her slim legs wide. Kathy gazed between them, seeing the tendons stretch. Cindy's young cunt seemed to be throbbing.

Robert climbed onto the couch with his sister, his cock straining hard, pre-cum dripping from the swollen head. Kathy's eyes blurred as she saw Robert press the head of his cock into the slippery lips of Cindy's cunt.