Aha! A few seconds later and a second shot with the flash stopped the movement and revealed the occupant/resident of that fairly new box.
It's Jazz in one of her favorite spots . . inside of a box. I'm not sure why cats love boxes so much. It may be because they would seem to offer protection or safety or coziness. But they all have to try out any box that comes into the house. This one is even big enough to accomodate Blackwell. But Jazz tends to adopt and dominate the territory whenever a new one appears.