Everyone who is owned by a cat knows what happens when you bring a new box into the house. It is like Kitty Christmas. The first thing they have to do is get inside like a child with a new playhouse. But why are cats so fascinated by a simple empty box? I suppose there are a number of things at “play” here.
I think the main reason is that cats love to play. The reason that they have an instinct for play is probably because it helps them practice for survival. Attacking their housemates, assuming it is not for reasons of dominance or territory, is practice for the hunt. Playing in a box is just an extension of that.
A box offers something a wild cat is looking for: stealth. Nevermind that they are not wild cats, they don’t know that. From inside a box a cat can see but not be seen. It is a great place to lie in wait until their prey is close and then pounce. It also offers a bit of protection from other “wild” household pets that might want to attack them.
Finally, cats are great nappers. Curling up inside a box could feel very cozy for that afternoon nap and offer protection as well.

This is great. A box all to myself.

Okay Puck, We’ve waited long enough.

Ha, now I have the box.

Stretch…

Don’t even think about it, Frankie.

This is just my size.

I wonder if there is a trap door in this thing.

That’s weird that Chris just disappeared. Oh well, it’s my box now.
If anyone can shed more light on why cats love boxes, or if you just want to comment, I’d love to hear from you.