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

How direct his thinking , she thought.
They glided lower . . . lower . . .
There came a rushing sense of motion to their passage—blurred shadows of dunes, rocks lifting like islands. The 'thopter touched a dune top with a soft lurch, skipped a sand valley, touched another dune.
He's killing our speed against the sand , Jessica thought, and permitted herself to admire his competence.
"Brace yourself!" Paul warned.
He pulled back on the wing brakes, gently at first, then harder and harder. He felt them cup the air, their aspect ratio dropping faster and faster. Wind screamed through the lapped coverts and primaries of the wings' leaves.
Abruptly, with only the faintest lurch of warning, the left wing, weakened by the storm, twisted upward and in, slamming across the side of the 'thopter. The craft skidded across a dune top, twisting to the left. It tumbled down the opposite face to bury its nose in the next dune amid a cascade of sand. They lay stopped on the broken wing side, the right wing pointing toward the stars.
Paul jerked off his safety harness, hurled himself upward across his mother, wrenching the door open. Sand poured around them into the cabin, bringing a dry smell of burned flint. He grabbed the pack from the rear, saw that his mother was free of her harness. She stepped up onto the side of the right-hand seat and out onto the 'thopter's metal skin. Paul followed, dragging the pack by its straps.
"Run!" he ordered.
He pointed up the dune face and beyond it where they could see a rock tower undercut by sandblast winds.
Jessica leaped off the 'thopter and ran, scrambling and sliding up the dune. She heard Paul's panting progress behind. They came out onto a sand ridge that curved away toward the rocks.
"Follow the ridge," Paul ordered. "It'll be faster."
They slogged toward the rocks, sand gripping their feet.
A new sound began to impress itself on them: a muted whisper, a hissing, an abrasive slithering.
"Worm," Paul said.
It grew louder.
"Faster!" Paul gasped.
The first rock shingle, like a beach slanting from the sand, lay no more than ten meters ahead when they heard metal crunch and shatter behind them.
Paul shifted his pack to his right arm, holding it by the straps. It slapped his side as he ran. He took his mother's arm with his other hand. They scrambled onto the lifting rock, up a pebble-littered surface through a twisted, wind-carved channel. Breath came dry and gasping in their throats.
"I can't run any farther," Jessica panted.
Paul stopped, pressed her into a gut of rock, turned and looked down onto the desert. A mound-in-motion ran parallel to their rock island —moonlit ripples, sand waves, a cresting burrow almost level with Paul's eyes at a distance of about a kilometer. The flattened dunes of its track curved once—a short loop crossing the patch of desert where they had abandoned their wrecked ornithopter.
Where the worm had been there was no sign of the aircraft.
The burrow mound moved outward into the desert, coursed back across its own path, questing.
"It's bigger than a Guild spaceship," Paul whispered. "I was told worms grew large in the deep desert, but I didn't realize . . . how big."
"Nor I," Jessica breathed.
Again, the thing turned out away from the rocks, sped now with a curving track toward the horizon. They listened until the sound of its passage was lost in gentle sand stirrings around them.
Paul took a deep breath, looked up at the moon-frosted escarpment, and quoted from the Kitab al-Ibar: "Travel by night and rest in black shade through the day." He looked at his mother. "We still have a few hours of night. Can you go on?"
"In a moment."
Paul stepped out onto the rock shingle, shouldered the pack and adjusted its straps. He stood a moment with a paracompass in his hands.
"Whenever you're ready," he said.
She pushed herself away from the rock, feeling her strength return. "Which direction?"
"Where this ridge leads." He pointed.
"Deep into the desert," she said.
"The Fremen desert," Paul whispered.
And he paused, shaken by the remembered high relief imagery of a prescient vision he had experienced on Caladan. He had seen this desert. But the set of the vision had been subtly different, like an optical image that had disappeared into his consciousness, been absorbed by memory, and now failed of perfect registry when projected onto the real scene. The vision appeared to have shifted and approached him from a different angle while he remained motionless.