you don't even have to know whether or not there's a cat in there

Maybe not - but I can assure you that no one could be near a cat in a box and not know about it. The soundproofing has yet to be invented that could drown out that noise! I believe that even profound deafness would not be proof against the sound of an incarcerated moggy.

As to getting the animal in there in the first place, every cat has its price. For one of mine, it is cucumber - of which she is inordinately fond. But for all three, cheese would do the trick - two will attempt fratricide in order to get at any sort of cheese (except Parmesan) whilst the third will use any sort of confidence trick for the chance to get even a nibble of the stuff. (That's the female one, of course )

Their best trick, of course, is to eat plenty of cheese and then sit by a mousehole with bated breath.