"The air of expectation had even spread to the ravens who inhabited the Tower of Art, eight hundred feet high and reputedly the oldest building in the world. Its crumbling stones supported thriving miniature forests high above the city's rooftops. Entire species of beetles and small mammals had evolved up there and, since people rarely climbed it these days owing to the tower's distressing tendency to sway in the breeze, the ravens had it all to themselves. Now they were flying around it in a state of some agitation, like gnats before a thunderstorm."
"These weren't ordinary ants. Centuries of magicalleakage into the walls of the University had done strange things to them. Some of them were pulling very small carts, some of them were riding beetles, but all of them were leaving the University as quickly as possible. The grass on the lawn rippled as they passed.
He looked up as an elderly striped mattress was extruded from an upper window and flopped down onto the flagstones below. After a pause, apparently to catch its breath, it rose a little from the ground. Then it started to float purposefully across the lawn and bore down on Rincewind, who managed to jump out of its way just in time. He heard a high-pitched chittering and caught a glimpse of thousands of determined little legs under the bulging fabric before it hurtled onward. Even the bedbugs were on the move, and in case they didn't find such comfortable quarters wlsewhere they were leaving nothing to chance. One of them waved at him and squeaked a greeting."
"A gritty noise made him look across the lawn.
There was no natural explanation of this. With incredible slowness, easing themselves down parapets and drainpipes in total silence except for the occassional scrape of stone on stone, the fargoyles were leaving the roof.
It's a shame that Rincewind had never seen poor quality stop-motion photography, because then he would have known exactly how to describe what he was seeing. the creatures didn't exactly move, but they managed to progress in a series of high speed tableaux, and lurched past him in a spindly procession of beaks, manes, wings, claws and pigeon droppings.
"What's happening?" he squeeked.
A thing with a goblin's face, harpy's body and hen's legs turned its head in a series of little jerks and spoke in a voice like the peristalsis of mountains (although the deep resonant effect was rather spoiled because, of course, it couldn't close its mouth)."
I love the mental imagery these paragraphs conjures up!