Naughty Nancy had been to my place a couple of times before.  She texted me one day and said she wanted to try something a little more risque.  I told her to come over the next day and I would pose her on her knees at the glory hole as if she were waiting on someone.  What I didn't tell her was that I invited a friend of mine to come stand at the hole.  She was pleasantly surprised and never saw his face before or since.