Movement -

M.C. Ecsher wrote in a letter to his son Arthur, on May 28, 1955:

   " What a fantastic experience is it on a freighter like this, when waking up at night in your own cabin you are suddenly able to account for that contrast with your immovable bed on land, in which you're used to lying still and horizontally, while your bed at sea is continuously rolling around that horizontality."

       Having kittens is like that.  The world is not still for them, or what they create is not still.   They take what has been motionless for years, and bounce it across the floor on their paws.  The whole house is rolling on a freighter, and vertical and horizontal are rounded here.