"If he's busy, I can come back later," Joan demurs, looking a trifle uncertain, as though she wants to be persuaded otherwise. As though she's been very much looking forward to their 'game'.

No point in making it too easy for Molokov. It would make her suspicious in his place. And it allows her a moment to pass her hand through her hair to neaten it, imply that the chess game had been something more intimate. The more important she seems to be, the more incautious Molokov is likely to be in reeling her in.