I don't think I've drunk enough beer to understand that.
There are, it has been said, two types of people in the world. There are those who, when presented with a glass that is exactly half full, say: this glass is half full. And then there are those who say: this glass is half empty. The world belongs, however, to those who can look at the glass and say: What's up with this glass? Excuse me? Excuse me? This is my glass? I don't think so. My glass was full! And it was a bigger glass! Who's been pinching my beer?
Well, basically there are two sorts of opera," said Nanny, who also had the true witch's ability to be confidently expert on the basis of no experience whatsoever. "There's your heavy opera, where basically people sing foreign and it goes like "Oh oh oh, I am dyin', oh I am dyin', oh oh oh, that's what I'm doin'", and there's your light opera, where they sing in foreign and it basically goes "Beer! Beer! Beer! Beer! I like to drink lots of beer!", although sometimes they drink champagne instead. That's basically all of opera, reely.
Nanny Ogg could see the future in the froth on a beer mug. It invariably showed that she was going to enjoy a refreshing drink which she almost certainly was not going to pay for.