Silver injections?
No wonder Soren is so subdued. Raking my eyes over his limp and rather lifeless form, I at last understand the reason for Soren's obedience to Azrael, and quite possibly why Azrael managed to capture Soren in the first place. Silver injections- likely dilute ones, (as I doubt Azrael would want to kill Soren just yet, else he would have no incentive for his game) are enough to knock even the strongest vampire off their feet. Including Soren.
It is a medieval tactic of control, ones angels used to use on the battlefields of war when the opportunity arose- pack a warrior with a handful of silver filled needles and you were all set. Issues later arose of course, the first being it was particularly hard to manoeuvre a battlefield when needles were being thrown let right and centre, and the second being that it was a huge waste of valuable materials that didn't even necessarily kill the vampire.
