Things were a little fraught in Unseen University. The wizards were scuttling from building to building, glancing at the sky.
The problem, of course, was the frogs. Not rains of frogs, which were uncommon now in Ankh-Morpork, but specifically foreign treefrogs from the humid jungles of Klatch. They were small, brightly coloured, happy little creatures who secreted some of the nastiest toxins in the world, which is why the job of looking after the large vivarium where they happily passed their days was given to first-year students, on the basis that if they got things wrong there wouldn't be too much education wasted.
Very occasionally a frog was removed from the vivarium and put into a rather smaller jar where it briefly became a very happy frog indeed, and then went to sleep and woke up in that great big jungle in the sky.
And thus the University got the active ingredient which it made up into pills and fed to the Bursar, to keep him sane. At least, apparently sane, because nothing was that simple at good old UU. In fact he was incurably insane and hallucinated more or less continuously, but by a remarkable stroke of lateral thinking his fellow wizards had reasoned that, in that case, the whole business could be sorted out if only they could find a formula that caused him to hallucinate that he was completely sane*
[* This is a very common hallucination, shared by most people.]
This had worked well. There had been a few false starts. For several hours, at one point, he had hallucinated that he was a bookcase. But now he was permanently hallucinating that he was a bursar, and that almost made up for the small side-effect that also led him to hallucinate that he could fly.
Of course, many people in the universe have also had the misplaced belief that they can safely ignore gravity, mostly after taking some local equivalent of dried frog pills, and this has led to much extra work for elementary physics and caused brief traffic jams in the street below. When a wizard hallucinates that he can fly, things are different.
'Bursaar! You come down here right this minute!' Arch-chancellor Mustrum Ridcully barked through his megaphone. 'You know what I said about goin' higher than the walls!' ached the pointy ears of the dwarfs.
'Can we?'
'Damned if I know. I can't.'
'Yeah, but if you could, you wouldn't say. I wouldn't say, if I could.'
'Can you?'
'No!'
'Ah-ha!'
It came to the ears of the Night Watch of the city guard, as they did gate duty at ten o'clock on an icy night. Gate duty in Ankh-Morpork was not taxing. It consisted mainly of waving through anything that wanted to go through, although traffic was minimal in the dark and freezing fog.
They hunched in the shelter of the gate arch, sharing one damp cigarette.
'You can't turn something into something else,' said Corporal Nobbs. The Alchemists have been trying it for years.'
They can gen'rally turn a house into a hole in the ground,' said Sergeant Colon.
That's what I'm talking about,' said Corporal Nobbs. 'Can't be done. It's all to do with... elements. An alchemist told me. Everything's made up of elements, right? Earth, Water, Air, Fire and... sunnink. Well-known fact. Everything's got 'em all mixed up just right.'
He stamped his feet in an effort to get some warmth into them.
'If it was possible to turn lead into gold, everyone'd be doing it,' he said.
'Wizards could do it,' said Sergeant Colon.
'Oh, well, magic,' said Nobby dismissively.
A large cart rumbled out of the yellow clouds and entered the arch, splashing Colon as it wobbled through one of the puddles that were such a feature of Ankh-Morpork's highways.
'Bloody dwarfs,' he said, as it continued on into the city. But he didn't say it too loudly.
There were a lot of them pushing that cart,' said Corporal Nobbs reflectively. It lurched slowly round a corner and was lost to view.
'Prob'ly all that gold,' said Colon.
'Hah. Yeah. That'd be it, then.'
And the rumour came to the ears of William de Worde, and in a sense it stopped there, because he dutifully wrote it down.
It was his job. Lady Margolotta of Uberwald sent him five dollars a month to do it. The Dowager Duchess of Quirm also sent him five dollars. So did King Verence of Lancre, and a few other Ramtop notables. So did the Seriph of Al Khali, although in his case the payment was half a cartload of figs, twice a year.