Light travels slowly on the Disc and is slightly heavy, with a tendency to pile up against high mountain ranges. Research wizards have speculated that there is another, much speedier type of light which allows the slower light to be seen, but since this moves too fast to see they have been unable to find a use for it.

This does mean that, despite the Disc being flat, everywhere does not experience the same time at, (or want of a better term, the same time. When it was so late at night in Ankh-Morpork that it was early in the morning, elsewhere it was...

... but there were no hours here. There was dawn and dusk, morning and afternoon, and presumably there was midnight and midday, but mainly there was heat. And redness. Something as artificial and human as an hour wouldn't last five minutes here. It would be dried out and shrivelled up in seconds.

Above all, there was silence. It was not the chilly, bleak silence of endless space, but the burning organic silence you get when, across a thousand miles of shimmering red horizons, everything is too tired to make a sound.

But, as the ear of observation panned across the desert, it picked up something like a chant, a reedy little litany that beat against the all-embracing silence like a fly bumping against the windowpane of the universe.

The rather breathless chanter was lost to view because he was standing in a hole dug in the red earth; occasionally some earth was thrown up on the heap behind him. A stained and battered pointy hat bobbed about in time with the tuneless tune. The word 'Wizzard' had, perhaps, once been embroidered on it in sequins. They had fallen off, but the word was still there in brighter red where the hat's original colour showed through. Several dozen small flies orbited it.

The words went something like this:

'Grubs! That's what we're going to eat! That's why they call it grub! And what're we doing to get the grub? Why, we're grubbing for it! Hooray!' Another shovelful of earth arced on to the heap, and the voice said, rather more quietly: 1 wonder if you can eat flies?'