You need to believe in things that aren't true. How else can they become?

They obeyed, as wise men do when a woman puts her foot down . . .

I hate cats." Death's face became a little stiffer, if that were possible. The blue glow in his eye sockets flickered red for an instant. "I SEE," he said. The tone suggested that death was too good for cat haters.

Voodoo is a very interesting religion for the whole family, even those members of it who are dead.

I think when people mean that Discworld books have become darker they really mean the series is growing up. In 'The Colour of Magic' most of the city is set alight. It's a joke, in much the same way that the Earth is destroyed almost at the start of Douglas Adams's 'The Hitchhikers Guide to the Galaxy.'

Everyone's heard of Erwin Schrodinger's famous thought experiment. You put a cat in a box with a bottle of poison, which many people would suggest is about as far as you need to go.

What did I tell you about Mister Safety Catch?' said Vimes weakly. When Mister Safety Catch Is Not On, Mister Crossbow Is Not Your Friend,' recited Detritus, saluting.