Interesting Conversation With My Wife

This weekend my wife and I went to an adult toy store to have a little fun. We looked at all the dildos, vibrators, cock rings and pocket pussies and were giggling like a couple of school kids, especially the enormous cocks that were closer to an arm size than a penis size. One of the things we bought was a little deck of cards that had sex things to try (we'd done lot of them) and also just conversation starters. One of the questions was "what is your naughtiest fantasy?" The first one that popped into my head was the fantasy described in my previous post. Although my SIL did watch us fucking, none of us acknowledged it nor spoke of it. Well I told my wife that she may be shocked by my naughtiest fantasy. She insisted that I tell her, and I said "once I say it, it can't be unsaid." I don't know what she was expecting, but said "come on I can handle it" So I told her "I fantasize about your sister watching us fuck while she masturbates right next to us."

Well, her jaw hit the floor! She was shocked, but had a horny look in her eye. "Do you want me to ask if she will?" It was my turn to be shocked. "She's your sister, you do what you want" I reminded her that once she asks, she can't "un-ask" She thought that her sister would be flattered. When we got home from our shopping trip, we were as horny as hell, and made up for lost time, but I've shot 3 more loads masturbating to the thought that this may come true. I can't get it out of my head. Her sister and our niece will be coming to town for spring break. I'm hoping that grandma and grandpa will watch our niece so we can have a few cocktails with my SIL and maybe be bold enough to ask the question.

I'd like a little input from the ladies, how would you react if your sister asked you to masturbate while she fucked her husband in front of you? Is that something that would turn you on? Please let me know.