Hang onto the keys for your friend’s sub.  Benefits:

– It teaches him to be very nice to her friends.  She can let him know who has it, or just leave that open.  It is fun, though to show it off to him, so he knows, and stays submissive

– you can help encourage him to remain submissive if he ever wants moments of release

– It makes it easier for her to keep him in chastity despite how much he might BEG or whine

– It intensifies the risk as a couple, which heightens the teasing even more

– she will be grateful to you and willing to try new challenges with you.

– what an extra tease for your husband, knowing you are holding onto another’s set of keys!