Sirius wanted to reach out, brush her hair out of her face- but she was right. People were looking a bit too interested in what was going on. So he drummed his fingers on his knee, letting them nudge against hers for a brief moment. Hm.
An idea struck him and he gave her a lopsided grin. "Do you, by any chance, know about the Room of Requirement? Because...very difficult for people to eavesdrop there," he whispered back.