Hermione was generally very good about planning out her studies so that she wasn't caught with things out, but she'd been going over her translation of Dumbledore's notes again, the bit about the Cup and the Diadem, and had forgotten that the blueprints Griphook had drawn for them that she'd been going over earlier with Harry and Ron were still unrolled on the table.
When he spoke, her eyes went wide for a moment, and she snapped closed her notes and reached for the map, starting to roll it up. She said, "Nothing important," and sounded hurried and caught, and for all the world like she wished he wouldn't ask any more questions about it, even though she knew he would.