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

Idaho was with us in the vision , he remembered. But now Idaho is dead .
"Do you see a way to go?" Jessica asked, mistaking his hesitation.
"No," he said, "But we'll go anyway."
He settled his shoulders more firmly in the pack, struck out up a sand-carved channel in the rock. The channel opened onto a moonlit floor of rock with benched ledges climbing away to the south.
Paul headed for the first ledge, clambered onto it. Jessica followed.
She noted presently how their passage became a matter of the immediate and particular—the sand pockets between rocks where their steps were slowed, the wind-carved ridge that cut their hands, the obstruction that forced a choice: Go over or go around? The terrain enforced its own rhythms. They spoke only when necessary and then with the hoarse voices of their exertion.
"Careful here—this ledge is slippery with sand."
"Watch you don't hit your head against this overhang."
"Stay below this ridge; the moon's at our backs and it'd show our movement to anyone out there."
Paul stopped in a bight of rock, leaned the pack against a narrow ledge.
Jessica leaned beside him, thankful for the moment of rest. She heard Paul pulling at his stillsuit tube, sipped her own reclaimed water. It tasted brackish, and she remembered the waters of Caladan—a tall fountain enclosing a curve of sky, such a richness of moisture that it hadn't been noticed for itself . . . only for its shape, or its reflection, or its sound as she stopped beside it.
To stop , she thought. To rest . . . truly rest .
It occurred to her that mercy was the ability to stop, if only for a moment. There was no mercy where there could be no stopping.
Paul pushed away from the rock ledge, turned, and climbed over a sloping surface. Jessica followed with a sigh.
They slid down onto a wide shelf that led around a sheer rock face. Again, they fell into the disjointed rhythm of movement across this broken land.
Jessica felt that the night was dominated by degrees of smallness in substances beneath their feet and hands—boulders or pea gravel or flaked rock or pea sand or sand itself or grit or dust or gossamer powder.
The powder clogged nose filters and had to be blown out. Pea sand and pea gravel rolled on a hard surface and could spill the unwary. Rock flakes cut.
And the omnipresent sand patches dragged against their feet.
Paul stopped abruptly on a rock shelf, steadied his mother as she stumbled into him.
He was pointing left and she looked along his arm to see that they stood atop a cliff with the desert stretched out like a static ocean some two hundred meters below. It lay there full of moon-silvered waves—shadows of angles that lapsed into curves and, in the distance, lifted to the misted gray blur of another escarpment.
"Open desert," she said.
"A wide place to cross," Paul said, and his voice was muffled by the filter trap across his face.
Jessica glanced left and right—nothing but sand below.
Paul stared straight ahead across the open dunes, watching the movement of shadows in the moon's passage. "About three or four kilometers across," he said.
" Worms ," she said.
"Sure to be."
She focused on her weariness, the muscle ache that dulled her senses. "Shall we rest and eat?"
Paul slipped out of the pack, sat down and leaned against it. Jessica supported herself by a hand on his shoulder as she sank to the rock beside him. She felt Paul turn as she settled herself, heard him scrabbling in the pack.
"Here," he said.
His hand felt dry against hers as he pressed two energy capsules into her palm
She swallowed them with a grudging spit of water from her stillsuit tube.
"Drink all your water," Paul said. "Axiom: the best place to conserve your water is in your body. It keeps your energy up. You're stronger. Trust your stillsuit."
She obeyed, drained her catchpockets, feeling energy return. She thought then how peaceful it was here in this moment of their tiredness, and she recalled once hearing the minstrel-warrior Gurney Halleck say, "Better a dry morsel and quietness therewith than a house full of sacrifice and strife."
Jessica repeated the words to Paul.
"That was Gurney," he said.
She caught the tone of his voice, the way he spoke as of someone dead, thought: And well poor Gurney might be dead . The Atreides forces were either dead or captive or lost like themselves in this waterless void.
"Gurney always had the right quotation," Paul said. "I can hear him now: 'And I will make the rivers dry, and sell the land into the hand of the wicked; and I will make the land waste, and all that is therein, by the hand of strangers.' "
Jessica closed her eyes, found herself moved close to tears by the pathos in her son's voice.
Presently, Paul said: "How do you . . . feel?"
She recognized that his question was directed at her pregnancy, said: "Your sister won't be born for many months yet. I still feel . . . physically adequate."
And she thought: How stiffly formal I speak to my own son! Then, because it was the Bene Gesserit way to seek within for the answer to such an oddity, she searched and found the source of her formality: I'm afraid of my son; I fear his strangeness; I fear what he may see ahead of us, what he may tell me .
Paul pulled his hood down over his eyes, listened to the bug-hustling sounds of the night. His lungs were charged with his own silence. His nose itched. He rubbed it, removed the filter and grew conscious of the rich smell of cinnamon.
"There's melange spice nearby," he said.
An eider wind feathered Paul's cheeks, ruffled the folds of his burnoose. But this wind carried no threat of storm; already he could sense the difference.
"Dawn soon," he said.
Jessica nodded.
"There's a way to get safely across that open sand," Paul said. "The Fremen do it."
"The worms?"
"If we were to plant a thumper from our Fremkit back in the rocks here," Paul said. "It'd keep a worm occupied for a time."
She glanced at the stretch of moonlighted desert between them and the other escarpment. "Four kilometers worth of time?"
"Perhaps. And if we crossed there making only natural sounds, the kind that don't attract the worms . . . "
Paul studied the open desert, questing in his prescient memory, probing the mysterious allusions to thumpers and maker hooks in the Fremkit manual that had come with their escape pack. He found it odd that all he sensed was pervasive terror at thought of the worms. He knew as though it lay just at the edge of his awareness that the worms were to be respected and not feared . . . if . . . if . . .
He shook his head.
"It'd have to be sounds without rhythm," Jessica said.
"What? Oh. Yes. If we broke our steps . . . the sand itself must shift down at times. Worms can't investigate every little sound. We should be fully rested before we try it, though."
He looked across at that other rock wall, seeing the passage of time in the vertical moonshadows there. "It'll be dawn within the hour."
"Where'll we spend the day?" she asked.
Paul turned left, pointed. "The cliff curves back north over there. You can see by the way it's wind-cut that's the windward face. There'll be crevasses there, deep ones."
"Had we better get started?" she asked.
He stood, helped her to her feet. "Are you rested enough for a climb down? I want to get as close as possible to the desert floor before we camp."
"Enough." She nodded for him to lead the way.
He hesitated, then lifted the pack, settled it onto his shoulders and turned along the cliff.