From "Manual of Muad'Dib" by the Princess Irulan

What if there isn't one of the abandoned testing stations across there? he wondered. What if there are no Fremen, either, and the plants we see are only an accident?
Within the tent, Jessica awakened, turned onto her back and peered sidelong out the transparent end at Paul. He stood with his back to her and something about his stance reminded her of his father. She sensed the well of grief rising within her and turned away.
Presently she adjusted her stillsuit, refreshed herself with water from the tent's catchpocket, and slipped out to stand and stretch the sleep from her muscles.
Paul spoke without turning: "I find myself enjoying the quiet here."
How the mind gears itself for its environment , she thought. And she recalled a Bene Gesserit axiom: "The mind can go either direction under stress—toward positive or toward negative: on or off. Think of it as a spectrum whose extremes are unconsciousness at the negative end and hyperconsciousness at the positive end. The way the mind will lean under stress is strongly influenced by training ."
"It could be a good life here," Paul said.
She tried to see the desert through his eyes, seeking to encompass all the rigors this planet accepted as commonplace, wondering at the possible futures Paul had glimpsed. One could be alone out here , she thought, without fear of someone behind you, without fear of the hunter .
She stepped past Paul, lifted her binoculars, adjusted the oil lenses and studied the escarpment across from them. Yes, saguaro in the arroyos and other spiny growth . . . and a matting of low grasses, yellow-green in the shadows.
"I'll strike camp," Paul said.
Jessica nodded, walked to the fissure's mouth where she could get a sweep of the desert, and swung her binoculars to the left. A salt pan glared white there with a blending of dirty tan at its edges—a field of white out here where white was death. But the pan said another thing: water . At some time water had flowed across that glaring white. She lowered her binoculars, adjusted her burnoose, listened for a moment to the sound of Paul's movements.
The sun dipped lower. Shadows stretched across the salt pan. Lines of wild color spread over the sunset horizon. Color streamed into a toe of darkness testing the sand. Coal-colored shadows spread, and the thick collapse of night blotted the desert.
Stars!
She stared up at them, sensing Paul's movements as he came up beside her. The desert night focused upward with a feeling of lift toward the stars. The weight of the day receded. There came a brief flurry of breeze across her face.
"The first moon will be up soon," Paul said. "The pack's ready. I've planted the thumper."
We could be lost forever in this hellplace , she thought. And no one to know .
The night wind spread sand runnels that grated across her face, bringing the smell of cinnamon: a shower of odors in the dark.
"Smell that," Paul said.
"I can smell it even through the filter," she said. "Riches. But will it buy water?" She pointed across the basin. "There are no artificial lights across there."
"Fremen would be hidden in a sietch behind those rocks," he said.
A sill of silver pushed above the horizon to their right: the first moon. It lifted into view, the hand pattern plain on its face. Jessica studied the white-silver of sand exposed in the light.
"I planted the thumper in the deepest part of the crevasse," Paul said. "Whenever I light its candle it'll give us about thirty minutes."
"Thirty minutes?"
"Before it starts calling . . . a . . . worm."
"Oh. I'm ready to go."
He slipped away from her side and she heard his progress back up their fissure.
The night is a tunnel , she thought, a hole into tomorrow . . . if we're to have a tomorrow . She shook her head. Why must I be so morbid? I was trained better than that!
Paul returned, took up the pack, led the way down to the first spreading dune where he stopped and listened as his mother came up behind him. He heard her soft progress and the cold single-grain dribbles of sound—the desert's own code spelling out its measure of safety.
"We must walk without rhythm," Paul said and he called up memory of men walking the sand . . . both prescient memory and real memory.
"Watch how I do it," he said. "This is how Fremen walk the sand."
He stepped out onto the windward face of the dune, following the curve of it, moved with a dragging pace.
Jessica studied his progress for ten steps, followed, imitating him. She saw the sense of it: they must sound like the natural shifting of sand . . . like the wind. But muscles protested this unnatural, broken pattern: Step . . . drag . . . drag . . . step . . . step . . . wait . . . drag . . . step . . .
Time stretched out around them. The rock face ahead seemed to grow no nearer. The one behind still towered high.
"Lump! Lump! Lump! Lump!"
It was a drumming from the cliff behind.
"The thumper," Paul hissed.
Its pounding continued and they found difficulty avoiding the rhythm of it in their stride.
"Lump . . . lump . . . lump . . . lump . . ."
They moved in a moonlit bowl punctured by that hollowed thumping. Down and up through spilling dunes: step . . .drag . . . wait . . . step . . . Across pea sand that rolled under their feet: drag . . . wait . . . step . . .
And all the while their ears searched for a special hissing.
The sound, when it came, started so low that their own dragging passage masked it. But it grew . . . louder and louder . . . out of the west.
"Lump . . . lump . . . lump . . . lump . . . " drummed the thumper.
The hissing approach spread across the night behind them. They turned their heads as they walked, saw the mound of the coursing worm.
"Keep moving," Paul whispered. "Don't look back."
A grating sound of fury exploded from the rock shadows they had left. It was a flailing avalanche of noise.
"Keep moving," Paul repeating.
He saw that they had reached an unmarked point where the two rock faces—the one ahead and the one behind—appeared equally remote.
And still behind them, that whipping, frenzied tearing of rocks dominated the night.
They moved on and on and on . . . Muscles reached a stage of mechanical aching that seemed to stretch out indefinitely, but Paul saw that the beckoning, escarpment ahead of them had climbed higher.
Jessica moved in a void of concentration, aware that the pressure of her will alone kept her walking. Dryness ached in her mouth, but the sounds behind drove away all hope of stopping for a sip from her stillsuit's catchpockets.
"Lump . . . lump . . . "
Renewed frenzy erupted from the distant cliff, drowning out the thumper.
Silence!
"Faster," Paul whispered.
She nodded, knowing he did not see the gesture, but needing the action to tell herself that it was necessary to demand even more from muscles that already were being taxed to their limits—the unnatural movement . . .
The rock face of safety ahead of them climbed into the stars, and Paul saw a plane of flat sand stretching out at the base. He stepped onto it, stumbled in his fatigue, righted himself with an involuntary out-thrusting of a foot.
Resonant booming shook the sand around them.
Paul lurched sideways two steps.
"Boom! Boom!"
"Drum sand!" Jessica hissed.
Paul recovered his balance. A sweeping glance took in the sand around them, the rock escarpment perhaps two hundred meters away.
Behind them, he heard a hissing—like the wind, like a riptide where there was no water.
"Run!" Jessica screamed. "Paul, run!"
They ran.
Drum sound boomed beneath their feet. Then they were out of it and into pea gravel. For a time, the running was a relief to muscles that ached from unfamiliar, rhythmless use. Here was action that could be understood. Here was rhythm. But sand and gravel dragged at their feet. And the hissing approach of the worm was storm sound that grew around them.
Jessica stumbled to her knees. All she could think of was the fatigue and the sound and the terror.
Paul dragged her up.
They ran on, hand in hand.
A thin pole jutted from the sand ahead of them. They passed it, saw another.
Jessica's mind failed to register on the poles until they were past.
There was another—wind-etched surface thrust up from a crack in rock.
Another.
Rock!
She felt it through her feet, the shock of unresisting surface, gained new strength from the firmer footing.
A deep crack stretched its vertical shadow upward into the cliff ahead of them. They sprinted for it, crowded into the narrow hole.
Behind them, the sound of the worm's passage stopped.
Jessica and Paul turned, peered out onto the desert.
Where the dunes began, perhaps fifty meters away at the foot of a rock beach, a silver-gray curve broached from the desert, sending rivers of sand and dust cascading all around. It lifted higher, resolved into a giant, questing mouth. It was a round, black hole with edges glistening in the moonlight.
The mouth snaked toward the narrow crack where Paul and Jessica huddled. Cinnamon yelled in their nostrils. Moonlight flashed from crystal teeth.
Back and forth the great mouth wove.
Paul stilled his breathing.
Jessica crouched staring.
It took intense concentration of her Bene Gesserit training to put down the primal terrors, subduing a race-memory fear that threatened to fill her mind.
Paul felt a kind of elation. In some recent instant, he had crossed a time barrier into more unknown territory. He could sense the darkness ahead, nothing revealed to his inner eye. It was as though some step he had taken had plunged him into a well . . . or into the trough of a wave where the future was invisible. The landscape had undergone a profound shifting.
Instead of frightening him, the sensation of time-darkness forced a hyper-acceleration of his other senses. He found himself registering every available aspect of the thing that lifted from the sand there seeking him. Its mouth was some eighty meters in diameter . . . crystal teeth with the curved shape of crysknives glinting around the rim . . . the bellows breath of cinnamon, subtle aldehydes . . . acids . . .
The worm blotted out the moonlight as it brushed the rocks above them. A shower of small stones and sand cascaded into the narrow hiding place.
Paul crowded his mother farther back.
Cinnamon!
The smell of it flooded across him.