I'm now kind of waiting for Sirius to come into action again.
He spent all day under a bed. We placed a food bowl there for a while, and a bowl of water. He ate and drank. Somehow, I would think that he needs to get rid of some stuff by now.
So, hoping he'll use the safety of darkness to visit the litterbox.
And, sort of hoping he will be wanting some interaction with his human, or with Luna. Would be good for him.