The dream was long enough ago, now, that By certainly doesn't instantly recognize that voice. But he does recognize the look on Benedict's face as one of alarm. And a particular type of alarm; By has learned by now that the lad looks different if he's worried for himself versus if he's worried for others. That's not the despairing agony of the latter; that's the anxious stewing of the former.

So he acts at once. There's a rack of clothes beside them, one that stretches from floor to ceiling, that Benedict could duck into and conceal himself thoroughly; By flicks his eyes towards it. And then he turns to the shopkeep, and says, "These powders here - " And he draws the man's attention in a direction opposite that potential hiding place.