First Thoughts are the everyday thoughts. Everyone has those. Second Thoughts are the thoughts you think about the way you think. People who enjoy thinking have those. Third Thoughts are thoughts that watch the world and think all by themselves. They’re rare, and often troublesome. Listening to them is part of witchcraft.

There are many horrible sights in the multiverse. Somehow, though, to a soul attuned to the subtle rhythms of a library, there are few worse sights than a hole where a book ought to be.

You can't remember the plot of the Dr Who movie because it didn't have one, just a lot of plot holes strung together. It did have a lot of flashing lights, though.

When I was a kid, I read the science-fiction shelves, and I read the fantasy shelves.

I think that sick people in Ankh-Morpork generally go to a vet. It's generally a better bet. There's more pressure on a vet to get it right. People say "it was god's will" when granny dies, but they get angry when they lose a cow.

Here's what I suggest," he said. "You pretend that rats can think, and I'll promise to pretend that humans can think, too.

Sooner or later we're all someone's dog.