Mark muted the basketball game as Joy, naked, walked into the home theatre. "I just wondered," he said, "why, when Kate saw me with the butt plug in my mouth, it didn't affect her?"
"Nice to see you take an interest in my work at last," said Joy dryly.
"I always said I supported your work," he muttered.
"And you did, unwittingly." She sat down on the other end of the couch, out of reach. "Firstly, Kate knew not to look at it for long. It takes time to take effect: you were looking at it for the whole time you were fucking me, which was probably much longer than you realized. Also, you're both susceptible to different frequencies, so we figured it was probably safe. And if we'd been wrong, it just would have made her submissive briefly and left me in control of her orgasms, so I thought it was worth the risk."
"Briefly? It's been more than a month, and I still can't come without your permission!"
Joy shrugged. "You have my permission to come an hour from now. I know you watch porn in your room. Satisfied?"
"Not really," he said, though he felt his cock start to stiffen. "What do you mean about my supporting your work?"
"Remember the fight we had about a year ago, when you wasted all that money on a new bike? That's when I started using you as an experimental subject. Blink rate, alpha rhythms, colour sensitivity, and so on."