"It’s a type of sexual magic that creates a powerful bond with your chosen six.  Groups of three usually.  Three you already had – I had no doubt that you would choose to serve Mistress Narcissa and Master Draco.  You were already bonded to them, in a way, because of me.  You chose the second three on your own.  Once you named them, it bonded them to you as well.  You ache for Yaxley, don’t you?" he asked softly, and she nodded, surprised he knew.