Looks like a spirity kind of apparition outside the hideaway to the left. This hideaway was Gizmo the cats favourite hideaway when he was alive. Lavender went into it for the first time today. A year after he was first diagnosed with cancer. It has been out all this time, but I guess she wanted to explore it. It was clean and sterilized after he passed.
There is nothing in the windows and no windows open and no vent in the bedroom near the windows.