Outside the boundaries of the universes lie the raw realities, the couldhave-beens, the might-bes, the neverweres, the wild ideas, all being created and uncreated chaotically like elements in fermenting supernovas.
Just occasionally where the walls of the worlds have worn a bit thin, they can leak in.
And reality leaks out.
The effect is like one of those deep-sea geysers of hot water, around which strange submarine creatures find enough warmth and food to make a brief, tiny oasis of existence in an environment where there shouldn't be any existence at all.
The idea of Holy Wood leaked innocently and joyfully into the Discworld.
And reality leaked out.
And was found. For there are Things outside, whose ability to sniff out tiny frail conglomerations of reality made the thing with the sharks and the trace of blood seem very boring indeed. They began to gather.
A storm slid in across the sand dunes but, where it reached the low hill, the clouds seemed to curve away. Only a few drops of rain hit the parched soil, and the gale became nothing more than a faint breeze.
It blew sand over the long-dead remains of afire.
Further down the slope, near a hole that was now big enough for, say, a badger, a small rock dislodged itself and rolled away.
A month went by quickly. It didn't want to hang around.
The Bursar knocked respectfully at the Archchancellor's door and then opened it.
A crossbow bolt nailed his hat to the woodwork.
The Archchancellor lowered the bow and glared at him.
'Bloody dangerous thing to do, wasn't it?' he said. 'You could have caused a nasty accident.'
The Bursar hadn't got where he was today, or rather where he had been ten seconds ago, which was where a calm and self-assured personality was, rather than where he was now, which was on the verge of a mild heart attack, without a tremendous ability to recover from unexpected upsets.
He unpinned his hat from the target chalked on the ancient woodwork.
'No harm done,' he said. No voice could be as calm as that without tremendous effort. 'You can barely see the hole. Why, er, are you shooting at the door, Master?'
'Use your common sense, man! It's dark outside and the damn walls are made of stone. You don't expect me to shoot at the damn walls?'
'Ah,' said the Bursar. 'The door is, er, five hundred years old, you know,' he added, with finely-tuned reproach.
'Looks it,' said the Archchancellor, bluntly. 'Damn great black thing. What we need around here, man, is a lot less stone and wood and a bit more jolliness. A few sportin' prints, yer know. An ornament or two.'
'I shall see to it directly,' lied the Bursar smoothly. He remembered the sheaf of papers under his arm. 'In the meantime, Master, perhaps you would care to-'
'Right,' said the Archchancellor, ramming his pointed hat on his head. 'Good man. Now, got a sick dragon to see to. Little devil hasn't touched his tar oil for days.'
'Your signature on one or two of-' the Bursar burbled hurriedly.
'Can't be havin' with all that stuff,' said the Archchancellor, waving him away. 'Too much damn paper around here as it is. And-' He stared through the Bursar, as if he had just remembered something. 'Saw a funny thing this mornin',' he said. 'Saw a monkey in the quad. Bold as brass.'
'Oh, yes,' said the Bursar, cheerfully. 'That would be the Librarian.'
'Got a pet, has he?'
'No, you misunderstand me, Archchancellor,' said the Bursar cheerfully. 'That was the Librarian.'
The Archchancellor stared at him.
The Bursar's smile began to glaze.