Because we have not opened this box since we placed the cat inside, and because we do not know when the flask of poison inside the box breaks, the cat is simultaneously alive and dead. Only by opening the box do we collapse the wave equation to a single eigenstate of alive or dead.

So, there’s a cat in that box over there?

Correct. A cat that is both alive and dead.

And the box is completely sealed?

Well, of course. If it were not sealed, we would be able to observe the system and the cat would no longer be in a superposition of both alive and dead. It would be one or the other.

And the cat has been in there how long?

About 20, maybe 30 minutes. Why?

Yeah, the cat’s dead.

How can you tell without opening the box?

Cats need air to live, you sick sadist.

Oh.

…

I should probably open the other boxes.

YOU DID THIS MORE THAN ONCE?!?!