[ID: Panels from two chapters of Natsume's Book of Friends. On the left is chapter 24, when Natsume meets Matoba and asks why he's draining youkai of blood. Matoba says, "How much do you know...? You don't seem to be just any kid from the neighborhood. Hm. I need you to tell me more." His constructed servant pops out of the bushes and tries to capture Natsume. On the right are panels from chapter 124 that closely parallel the ones to their left, showing Natsume asking Shinobu what Ban is doing at the auction. She says, "You know about him too? I figured you had weird instincts, but...how much have you figured out? Now then. What should I do with you?" She summons her constructed servant, which chases after Natsume. /end ID]
the question remains what shinobu's quasi-familiar would have done with natsume after catching him but putting that aside the matoba siblings' reactions to natsume knowing too much are beat-for-beat basically identical. "oh aren't you a little weirdo. what else do you know? let's sic a constructed servant on you about it." they went to the same childhood all right