"Charming," Snape declared in tones that dripped icicles of pure concentrated cynicism. "And to think, I had no idea either of you had such a lively interest in Astronomy. Perhaps I should have asked one of you to take up an entirely different Professorship." he drawled.
A sharp-edged smirk dawned. "Or perhaps your shared interests lay in areas far more ...earthly than Astronomy."
All the while, a stare as cold and black as the grave declared almost as clearly as speech, 'I'm not buying your story for a second'.
Fortunately for all concerned, Snape's sensitivity to Dark Magic - finely honed after a lifetime of his own private researches - wasn't reacting any worse than it usually did around either of them, so he really didn't feel that it was worth the consequences to Legilimens either of them.
"Whatever your motivation," he concluded in icy tones, "all-night excursions so very close to the start of term - especially the first term either of you have ever taught - are not acceptable behaviour for Professors," a glare at Caractacus, "and even less so for Heads of House," he turned the glare Eileen's way.
"Since this is the first occurrence, I shall let you both off with a warning. I assure you, I shall not be so lenient with a second transgression."