Frage
Das habe ich gefunden
Well in the dub, (which I've always thought was better in this show's case) when they say that, a thing pops up on the screen that says
Note: "Balse" is an incantation used to destroy the flying castle Laputa
As to why it's censored, it might be a video game reference and many references like that get censored in anime, probably because they couldn't get the rights to say it or something along those lines. Lucky Star is a perfect example of this as it happens frequently throughout the anime.