You know what they really need after all, despite it being only the two of them here? A gigantic mansion with thick walls where sound doesn't carry so infernally easy. This is a conclusion that Sebastian has reached completely apropos nothing.
Ciel might have heard his front door opening and closing, opening and closing a rather unwarranted amount of times during one single morning. It's like someone's stepping outside on some very quick business before coming right back in. Very mysterious, that.
There's one time during breakfast preparation where Sebastian doesn't make it out the door in time - he can't leave the tea to brew for an additional minute to go cough; he'll simply have to force himself not to until he's done with the te-- And, yes, well. If he's lucky, Ciel didn't hear that.
There's the usual "good morning" knock on Ciel's bedroom door before Sebastian sees himself in, as usual. Completely normal morning.]