"And most of the others have either shown before that they tend to throw in the towel in times of need, or at least have given sufficient reason to believe that they will do just that when push comes to shove. Why do you think he used Pettigrew the first time? For exactly the same reasons, of course. Also, apart from Bellatrix, very few Death Eaters master Occlumency. It's not a particularly common ability. So I could well imagine that he took a quick look inside one or the other head before making his selection. It didn't work for me, though, because I was always so well occluded that he didn't even know I was capable of it. So he had no reason to doubt me. I resolutely worked my way up and did whatever he asked me to do. Et voila, a faithful servant." 