Lupin had clearly not paid attention for a while there, looking at Severus, seemingly almost... mesmerised until he snapped out of it.

Severus' eyebrows quirked slightly as he wondered about the reason. He couldn't find any. At least not a reason that would make sense, other than Lupin might be more tired than he'd thought.

He would not contemplate other possible explanations.

"Whatever suits you." Maybe Lupin wanted to get out of the house after all, and Severus had no intention of talking the man out of it, if that would save him the bother of going here.