In fact the cat can also be alive when you oppen the box. The alive/dead at the same time occur only when the box is closed. The result is fixed and can't change once the box has been opened. Even if a vampire zombie cat could be really cool it's unfortunatly not possible (too bad). I confess that this is a really hard theme that I don't master really well but I know that this "experiment" is (volouterely?) overly reducteur of the double state phenomena and that it doesn't respect any scale. Nevertheless it is still a great way to explain a very complex phenomena quite easily.