He helped the Librarian up. There was a red glow in the ape's eyes. It had tried to steal his books. This was probably the best proof any wizard could require that the trolleys were brainless.

I can't be talking to a tree. If I was talking to a tree I'd be mad, and I'm not mad, so trees can't talk.

Down there - he said - are people who will follow any dragon, worship any god, ignore any inequity. All out of a kind of humdrum, everyday badness. Not the really high, creative loathsomeness of the great sinners, but a sort of mass-produced darkness of the soul. Sin, you might say, without a trace of originality. They accept evil not because they say yes, but because they don't say no.

See a pin and pick it up, and, all day long, you'll have a pin.

Personally, I think the best motto for an educational establishment is: 'Or Would You Rather Be a Mule?'

He found that he had this sudden desperate longing for the fuming, smoky streets of Ankh-Morpork, which was always at its best in the spring, when the gummy sheen on the turbid waters of the Ankh River had a special iridescence and the eaves were full of birdsong, or at least birds coughing rhythmically

This is space. It's sometimes called the final frontier. (Except that of course you can't have a final frontier, because there'd be nothing for it to be a frontier to, but as frontiers go, it's pretty penultimate . . .)