"Oh, well." He smiles humorlessly. "Knowing the invitation isn't knowing the precipitant. But that's not relevant. An attack in general, but, well, an attack by snake from that quarter wouldn't have been unexpected."
"True." He takes a sip, too, but of the juice. This is all getting a bit hard on his throat. His own fault, of course; he never could shut up and give a short answer. "You needn't go into the details, of course. But might I suggest that if it is related to what you take it for, the evidence suggests that I have in some way been exposed to to the same thing you have these memories of, whether or not I know it?" This, he hopes, will convey and so I can't judge you as well as and so I sort of need to know, yeah? and and so you might have one of these in you, too, but you can't rely on other people getting those shades, even when you're sure they're fellow serpents. "As am I. It's possible that knowing its nature might lead us to that answer, as well."
He leaves charms out in the common room every year with strongly-noted words about enforced personal and mutual responsibility. It's a toss-up whether the charms or the note is more effective. ;)