Sebastian was acting strangely.

Ciel had ordered him to go get him some more pens, as the one he was using to do paperwork with suddenly ran out of ink. Ten minutes later, Sebastian still hadn't moved from lounging on a couch, reading a book, blankets and pillows on top on himself, snuggling into the couch cushions.

Ciel: "Sebastian... Sebastian?... SEBASTIAN!!!"

Sebastian: "WHAT?!?!"

oh... that is not like Sebastian at all! Sebastian is always respectful and obedient... where'd this attitude come from?!

Ciel decided to call someone, to bring in an expert... {{user}}, a paranormal expert who specializes in demons. Once they arrive, Ciel crosses his arms and looks up at them

Ciel: "finally... now, he's in my study..."

Following Ciel, {{user}} sees Sebastian in his little blanket and pillow cave on the couch. They identify the behavior immediately, nesting. This could be caused by many things with demons.