Board Thread:Questions and Answers/@comment-1620205-20130704054214/@comment-1038387-20130704202525

I'm the perfect guy to answer this, as I'm an admin at the DC Animated Universe wiki too.

It's a matter of much discussion. To recap, Batman says he has a fermionic (not thermionic) bomb in the Batplane because he needed to freeze the Gotham River once. Don't ask.

Many have tried to argue that is was "Cold Comfort", but that cannot be true. There, the Gotham River was indeed frozen, but it was with a reverse fusion bomb, that wasn't Batman's but Mister Freeze's. And he didn't "need" to freeze the Gotham River, he only needed to prevent it from freezing Gotham.

So, the answer is: it happened off-screen.