Clicking her tongue in disappointment, Chrysalis answered "Fire breathing is a magical ability of theirs, one which is negated, as is all non-Changeling magic, when inside the boundaries of our hive. However, to help answer your other question, I have not allowed such potent magic go to waste. So I had some special chains based off the workings of Lord Tirek, nasty centaur man, we'll avoid him and his cell in Tartarus. Basically, those chains grow stronger the more magic is channeled into them, and every time the dragons try to breathe fire, it channels magic into them!"