[He glances to the ceiling, then back to the phial, which may almost be full by now.]

It's an effect of the moon. Much as it pulls on the tides, it pulls on our Blood and affects our moods and modes.

[A thoughtful pause.] I'd have to ask around and see if any other Vileblood has experienced similar sensations. It could be useful networking. Information is often the best currency, especially in a world where barter is the order of the day.

[The phial has filled by now. He'll carefully remove the cannula and pressing a pad of gauze to the mark it leaves, he'll tape it into place.]