This feature of the human mind may go back to the time, just after the meteorite hit, when the nocturnal mammals suddenly awoke in a world without dinosaurs. Their senses of hearing and sight, previously separate from each other because they had evolved at very different periods and in very different circumstances, would have become linked together. When their ears heard something strange, their visual sense would kick in and make them feel that they could see what was causing it. We inherited this tendency, but we interpret it in terms of the current culture: bogeymen, witches, maybe even dragons a few centuries ago, aliens with big black eyes today. The sexual link is straightforward, too: dreams about sex are very common anyway.
Oh, yes, one more thing: since we've all watched Close Encounters, we know exactly what an alien must look like ... just as everyone used to know that witches soared through the air on a broomstick. So our visual system knows what shape it should give to whatever it sees when we get that funny feeling that something is haunting us. And flying saucers have come on nicely, too, from being the rivet-studded things that were all the rage in galactic circles in the early Fifties.
Stories of people seeing ghosts may well have the same explanation. You've read the tales, you know what a ghost ought to look like (maybe you watched Ghostbusters or a Stephen King movie), and you're trying to sit up all night in the Haunted House. You're thinking about ghosts, about headless horsemen and Elizabethan ladies who walk through walls and go transparent, and then you start to doze off because it's 2 am and you've been up all night... The sleep paralysis circuit glitches ... Aaaaagh!
DON'T PLAY GOD
THE ARCHCHANCELLOR WAS RATHER QUIET OVER TEA.
Eventually he said, 'Can we stop this project, Ponder?'
'Er ... are you sure, sir?' 'Well, what is it achieving? I mean, really'? Y'know, I thought, all you had to do is get a world working, and before you could say "creation" there'd be some creature who'd stand up, getting a grip on its surroundings, gaze with a certain amount of intelligence and awe at the infinite sky and say...'
‘...that thing's getting bigger, I wonder if it's going to hit us,' said Rincewind.
'Rincewind, that remark was extremely cynical and accurate.'
'Sorry, Archchancellor.'
Bonder's lips were moving quietly as he worked things out.
'We could start running it down, yes. The thaumic reactor hasn't been putting so much into it in the last week. We've nearly used up the fuel.'
'Really?'
'The squash court will have a rather high thaumic index, sir, so whoever goes in to pull the switch will suffer a certain amount of...'
There was the sound of something spinning. The wizards looked at Rincewind's chair, which finally fell over on to the flagstones. Of its former occupant there was no sign, although there was the distant sound of a slamming door.
The Dean sniffed.
'Strange behaviour,' he said.
'I suggest we give it one more day of our time,' said Ridcully. 'I was hoping we might create a world, gentlemen, but instead it's clear to me that any life in this universe has to get used to living in ... in some kind of huge celestial snow globe. Fire and ice, ice and fire. Gentlemen, round worlds are intrinsically flawed. If there's any hidden gods on ours, they're pretty damn well hidden.'
'The Omnians say "Don't play God. He always wins",' said the Senior Wrangler.
'I dare say,' said Ridcully 'So ... one more day, gentlemen? And then we can get on with something sensible.'
The red sun rose quickly over the parched veldt. The apes stirred in their cave, which was little more than a rocky overhang, and saw the big black rectangle looming over them.
The Dean tapped it with his pointer
'Do try to pay attention today, will you?' He turned and chalked rapidly across the blackboard. 'Here we have R ... O ... C ... K, rock. Can anyone tell me what you do with it? Anyone? Anyone? Look, stop doing that, will you?' He tried to hit an ape with his virtual pointer, and then flung it away in disgust. It vanished.
'Filthy little devils,' he muttered.
'Not getting anywhere, Dean?' said Ridcully, appearing beside him.
Wo, Archchancellor. I've tried to explain to them that they've probably got just a few million years, and that's pretty hard to do in sign language, let me tell you. But the only word they know is S-E-X, and they don't waste time spelling it, oh no! For this I skipped breakfast?'
'Never mind. Let's see how the Senior Wrangler's getting on.'
'They're just bad copies of humans, if you ask me...'
The wizards vanished.
One of the apes knuckled over to the blackboard, and watched it disappear from view as HEX completed the spell.
He hadn't the faintest idea what had been happening, but he had been impressed by the stick that had been waved about. That seemed to have gone now. That didn't worry the ape, which knew about things vanishing, often, these days, a member of the clan would vanish overnight, with a lot of snarling in the shadows.
There was probably something you could do with a stick, he thought. Hopefully, it might involve sex.
He poked around in the debris and found not a stick but a dried-up thighbone, which had a sufficiently stick-like shape.
He rattled it on the ground a few times. It didn't do anything much. Then he reluctantly decided it would probably be impossible to mate with at the moment, and hurled it high into the air.
It rose, turning over and over.
When it fell, it knocked him unconscious.
The Senior Wrangler was sitting under a virtually-there beach umbrella when the other wizards arrived. He looked as downcast as the Dean.
A group of apes was playing in the surf.
'Worse than the lizards,' he said. 'They had some style, at least. When this lot pick up anything, they try to see if they can eat it. What's the point of that?'
'Well, I suppose they can find out if it's edible,' said Ridcully.
'But they just mess about,'said the Senior Wrangler. 'Oh, no ... here we go again ...'
There was a raucous shrieking as the tribe rushed out of the waves and swung up into the nearby mangrove trees. A shadow sped beyond the surf and headed back into the blue water, to an unregarded chorus of simian catcalls and mangrove seeds.
'Oh yes, and they like throwing things,' said the Senior Wrangler.
'Seafood is good for the brain, my granny always said,' said Ridcully.
'This lot couldn't eat too much of it, then. Yell, throw things, and prod stuff to see what it does, that's the extent of their capabilities. Oh, why didn't we discover the lizards earlier? They had class?'
'Wouldn't have stopped the snowball,' said Ridcully.