My BFF, my sister Pat and I were all enjoying a cuppa when Pat's cat Romeo declared war on a cardboard box. He was determined to defy the known Laws of Physics concerning mass and volume, fitting his entire body into a container the size of a Kleenex box. Shirley and Pat have six (!) cats between them, and assure me that if there's a box, there's gonna be a cat in it.
Further research reveals some of the theories about this: Back to the womb... the feeling of close confinement is calming and many others. The one that seems to make the most sense is that cats like a temperature between 86 and 97 degrees F., and cardboard is a great insulator. They can heat that box quickly... a warm cat is a happy cat.
Sister Pat says, "Forget your theories. Anyone who claims to be able to understand cats is a fraud." Let's ensure that our bidding isn't fraudulent. Ready?