Manhole covers explode all the time. But I can't remember any that sent up a 15-foot tower of cackling flames and gas in the middle of the West Village. Somewhere in the sewer is a dragon with a Jiffy Pop.
Your current favorite manhole fact: they're round so that they can't fall in the manhole, even when they're turned sideways. Your new favorite manhole fact: in Japan, they serve as canvasses for hundreds of beautiful, vibrant artworks: