They'll have to agree to disagree about magic, for now, because Kostos doesn't argue, only pulls a face that's subtle enough not to quite demand commentary and returns, too, to pulling at the splinter on the table. The joke, meanwhile, flies right over his head—not because he can't recognize a joke, but because he's only vaguely and barely aware that Anders might have been possessed at some point and, given the dearth of cases of mages coming back from possession, even less aware of former possession leaving any sort of imprint, which if true would have incredibly alarming implications for the viability of depossession as a solution in the future—

—all of which is a mental tangent he doesn't go on, because he doesn't get it. He assumes Anders' former company were rebel mages. Which also makes sense, and is also almost a joke, he supposes, enough to warrant twitching one side of his mouth in acknowledgment.

And then to just sort of sit there. He doesn't know what else to say.