Swapping sometimes begins even when you don't intend it to. I had bought my wife a new sex toy, an egg vibrator that had a wireless remote control that I could use even when we were out shopping or in a restaurant. It was great fun for us both making her squirm and moan while I manipulated the remote.
It was when she wore it hidden away inside under her shorts when we had friends over that things got a little crazy, well, a lot crazy. You'll just have to read what happened. You might want one yourself. You never know what might happen.