Anyway I was saying to Alice that it doesn't have to be someone we actually want (and probably shouldn't be, actually, since this isn't meant to work). We could demand someone loyal, implying that they're not and possibly making them distrust them. We could say we'd trade him for Barty Crouch's head on a platter. We could demand someone we have, and confuse them because presumably they know that person's gone from Azkaban, so if they're not with us, where are they -- right?

The question isn't, 'who do we want,' the question is, 'who is it to our advantage to ask for.'