Marla started to say something; she swallowed, looking at her son, who was trying to cover up his hard-on, then at the mirror on the floor. She saw her daughter's reflection in it, the crotch of Sally's panties.

Sally's giggle broke the tension.

"Oh, God!" Marla said throatily.

"You do it, Mother," Sally said, not in the least embarrassed.

"But… not in front of Bob," Marla managed to get out. "Not in front of anyone."

"Well," Sally replied, lifting her pretty face almost as a challenge, "I do."

Marla stared at her daughter, then at her son. She couldn't say anything. Sally was right. She did it, and they had seen her do it. She had no right to say a word. She turned and left.

In the living room, Marla tried to sort out the whirling thoughts in her mind, but the vision of her daughter with her skirt at her waist, and of her son's cock pressing at his pants, refused to leave her mind.

She wondered how often they had watched her, what they had seen, and what their thoughts were.

"Are you mad at us, Mom?"

Marla looked up and saw her son entering the room. Her eyes went immediately to the front of his pants. She didn't see a hard-on, but there was a lovely lump there. Behind him Sally peered at her.

Marla shook her head.

"Well, you shouldn't be, Mother," Sally said, walking past her brother and flouncing into a chair, drawing her feet up and crossing them. Her slim thighs were showing as she tucked her skirt between them, looking at her mother. "Why get mad at us for doing what you do?"

"I'm not… I'm not mad," Marla replied. "I think I understand it."

Bob sat down on the floor near his sister, lifting one knee and pulling it to his chest.

"I know you two have watched me," Marla went on in a low voice. "Hearing you, seeing the mirror, is enough to tell me that. Any other mother would probably be very angry with you, but I understand."