[He watches the test with interest, raising a brow at the color changing - first to the red he more commonly associates with what he inevitable came to call mana potions, and then to a pink that was wholly absent from the spectrum of concoctions he'd yet encountered. Still, he's not going to outright ask - if Cassian wanted him to know what that was all about, he'd tell him.]

I've a line on some of them, assuming I haven't been barred entry to the castle yet. You can keep the book - I've a copy of my own, and the full volume remains secure in the Belmont clan library. Is there anything else I can do to help you tonight?

[Given Cassian's connection to Hastur, there's a solid chance he's realized by now that Soma is a fellow consumer of souls - Soma hasn't and won't make the same connection, because Soma himself only vaguely registers it when he does it. Interestingly, though, none of the ones he holds are human - but there are quite a lot of monster and demon souls in there.]