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

Why not? she thought as she brushed at her robe. This was a likely place—deep in rock walls and facing another cliff some four kilometers away—far enough above the desert to avoid worms but close enough for easy access before a crossing.
She turned, seeing that Paul had the tent up, its rib-domed hemisphere blending with the rock walls of the fissure. Paul stepped past her, lifting his binoculars. He adjusted their internal pressure with a quick twist, focused the oil lenses on the other cliff lifting golden tan in morning light across open sand.
Jessica watched as he studied that apocalyptic landscape, his eyes probing into sand rivers and canyons.
"There are growing things over there," he said.
Jessica found the spare binoculars in the pack beside the tent, moved up beside Paul.
"There," he said, holding the binoculars with one hand and pointing with the other.
She looked where he pointed.
"Saguaro," she said. "Scrawny stuff."
"There may be people nearby," Paul said.
"That could be the remains of a botanical testing station," she warned.
"This is pretty far south into the desert," he said. He lowered his binoculars, rubbed beneath his filter baffle, feeling how dry and chapped his lips were, sensing the dusty taste of thirst in his mouth. "This has the feeling of a Fremen place," he said.
"Are we certain the Fremen will be friendly?" she asked.
"Kynes promised their help."
But there's desperation in the people of this desert , she thought. I felt some of it myself today. Desperate people might kill us for our water .
She closed her eyes and, against this wasteland, conjured in her mind a scene from Caladan. There had been a vacation trip once on Caladan—she and the Duke Leto, before Paul's birth. They'd flown over the southern jungles, above the weed-wild shouting leaves and rice paddies of the deltas. And they had seen the ant lines in the greenery—man-gangs carrying their loads on suspensor-buoyed shoulder poles. And in the sea reaches there'd been the white petals of trimaran dhows.
All of it gone.
Jessica opened her eyes to the desert stillness, to the mounting warmth of the day. Restless heat devils were beginning to set the air aquiver out on the open sand. The other rock face across from them was like a thing seen through cheap glass.
A spill of sand spread its brief curtain across the open end of the fissure. The sand hissed down, loosed by puffs of morning breeze, by the hawks that were beginning to lift away from the clifftop. When the sandfall was gone, she still heard it hissing. It grew louder, a sound that once heard, was never forgotten.
"Worm," Paul whispered.
It came from their right with an uncaring majesty that could not be ignored. A twisting burrow-mound of sand cut through the dunes within their field of vision. The mound lifted in front, dusting away like a bow wave in water. Then it was gone, coursing off to the left.
The sound diminished, died.
"I've seen space frigates that were smaller," Paul whispered.
She nodded, continuing to stare across the desert. Where the worm had passed there remained that tantalizing gap. It flowed bitterly endless before them, beckoning beneath its horizontal collapse of skyline.
"When we've rested," Jessica said, "we should continue with your lessons."
He suppressed a sudden anger, said: "Mother, don't you think we could do without . . ."
"Today you panicked," she said. "You know your mind and bindu-nervature perhaps better than I do, but you've much yet to learn about your body's prana-musculature. The body does things of itself sometimes, Paul, and I can teach you about this. You must learn to control every muscle, every fiber of your body. You need review of the hands. We'll start with finger muscles, palm tendons, and tip sensitivity." She turned away. "Come, into the tent, now."
He flexed the fingers of his left hand, watching her crawl through the sphincter valve, knowing that he could not deflect her from this determination . . . that he must agree.