I had one experience like this. Another couple who we really like had swapped with my wife and I several times. And the swap "guidelines" would be for everyone to finish and then we would take a break with some cocktails and something to eat. When everyone was ready for round 2 the wives would start to orally work on the other husband to get them hard enough to perform act 2. Out of the blue the other wife asks me and my wife if it was OK for her husband to take me into his mouth start the process. We were both stunned but I agreed to try it. To say the least it was interesting. Once you get used to watching another man blowing you it actually feels really great. Maybe it's because only a person with a penis knows best how to really suck another penis. I would think the same applies to a woman going down on another woman.