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

Pass within , she thought. An odd way of putting it. But the rest of it fitted into the cant well enough . And she felt a cynical bitterness at what she had done. Our Missionaria Protectiva seldom fails. A place was prepared for us in this wilderness. The prayer of the salat has carved out our hiding place. Now . . . I must play the part of Auliya, the Friend of God . . . Sayyadina to rogue peoples who've been so heavily imprinted with our Bene Gesserit soothsay they even call their chief priestesses Reverend Mothers .
Paul stood beside Chani in the shadows of the inner cave. He could still taste the morsel she had fed him—bird flesh and grain bound with spice honey and encased in a leaf. In tasting it he had realized he never before had eaten such a concentration of spice essence and there had been a moment of fear. He knew what this essence could do to him—the spice change that pushed his mind into prescient awareness.
"Bi-la kaifa," Chani whispered.
He looked at her, seeing the awe with which the Fremen appeared to accept his mother's words. Only the man called Jamis seemed to stand aloof from the ceremony, holding himself apart with arms folded across his breast.
"Duy yakha hin mange," Chani whispered. "Duy punra hin mange. I have two eyes. I have two feet."
And she stared at Paul with a look of wonder.
Paul took a deep breath, trying to still the tempest within him. His mother's words had locked onto the working of the spice essence, and he had felt her voice rise and fall within him like the shadows of an open fire. Through it all, he had sensed the edge of cynicism in her—he knew her so well!—but nothing could stop this thing that had begun with a morsel of food.
Terrible purpose!
He sensed it, the race consciousness that he could not escape. There was the sharpened clarity, the inflow of data, the cold precision of his awareness. He sank to the floor, sitting with his back against rock, giving himself up to it. Awareness flowed into that timeless stratum where he could view time, sensing the available paths, the winds of the future . . . the winds of the past: the one-eyed vision of the past, the one-eyed vision of the present and the one-eyed vision of the future—all combined in a trinocular vision that permitted him to see time-become-space.
There was danger, he felt, of overrunning himself, and he had to hold onto his awareness of the present, sensing the blurred deflection of experience, the flowing moment, the continual solidification of that-which-is into the perpetual-was.
In grasping the present, he felt for the first time the massive steadiness of time's movement everywhere complicated by shifting currents, waves, surges, and countersurges, like surf against rocky cliffs. It gave him a new understanding of his prescience, and he saw the source of blind time, the source of error in it, with an immediate sensation of fear.
The prescience, he realized, was an illumination that incorporated the limits of what it revealed—at once a source of accuracy and meaningful error. A kind of Heisenberg indeterminacy intervened: the expenditure of energy that revealed what he saw, changed what he saw.
And what he saw was a time nexus within this cave, a boiling of possibilities focused here, wherein the most minute action—the wink of an eye, a careless word, a misplaced grain of sand—moved a gigantic lever across the known universe. He saw violence with the outcome subject to so many variables that his slightest movement created vast shiftings in the pattern.
The vision made him want to freeze into immobility, but this, too, was action with its consequences.
The countless consequences—lines fanned out from this cave, and along most of these consequence-lines he saw his own dead body with blood flowing from a gaping knife wound.
My father, the Padishah Emperor, was 72 yet looked no more than 35 the year he encompassed the death of Duke Leto and gave Arrakis back to the Harkonnens. He seldom appeared in public wearing other than a Sardaukar uniform and a Burseg's black helmet with the imperial lion in gold upon its crest. The uniform was an open reminder of where his power lay. He was not always that blatant, though. When he wanted, he could radiate charm and sincerity, but I often wonder in these later days if anything about him was as it seemed. I think now he was a man fighting constantly to escape the bars of an invisible cage. You must remember that he was an emperor, father-head of a dynasty that reached back into the dimmest history. But we denied him a legal son. Was this not the most terrible defeat a ruler ever suffered? My mother obeyed her Sister Superiors where the Lady Jessica disobeyed. Which of them was the stronger? History already has answered.
—"In My Father's House" by the Princess Irulan
Jessica awakened in cave darkness, sensing the stir of Fremen around her, smelling the acrid stillsuit odor. Her inner timesense told her it would soon be night outside, but the cave remained in blackness, shielded from the desert by the plastic hoods that trapped their body moisture within this space.
She realized that she had permitted herself the utterly relaxing sleep of great fatigue, and this suggested something of her own unconscious assessment on personal security within Stilgar's troop. She turned in the hammock that had been fashioned of her robe, slipped her feet to the rock floor and into her desert boots.