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

He has talked enough , Jessica thought. I've the key to him. I could immobilize him with a word . She hesitated. But I cannot stop them all .
"You will answer to me then," Jessica said, and she pitched her voice in a twisting tone with a little whine in it and a catch at the end.
Jamis stared at her, fright visible on his face.
"I'll teach you agony," she said in the same tone. "Remember that as you fight. You'll have agony such as will make the gom jabbar a happy memory by comparison. You will writhe with your entire—"
"She tries a spell on me!" Jamis gasped. He put his clenched right fist beside his ear. "I invoke the silence on her!"
"So be it then," Stilgar said. He cast a warning glance at Jessica. "If you speak again, Sayyadina, we'll know it's your witchcraft and you'll be forfeit." He nodded for her to step back.
Jessica felt hands pulling her, helping her back, and she sensed they were not unkindly. She saw Paul being separated from the throng, the elfin-faced Chani whispering in his ear as she nodded toward Jamis.
A ring formed within the troop. More glowglobes were brought and all of them tuned to the yellow band.
Jamis stepped into the ring, slipped out of his robe and tossed it to someone in the crowd. He stood there in a cloudy gray slickness of stillsuit that was patched and marked by tucks and gathers. For a moment, he bent with his mouth to his shoulder, drinking from a catchpocket tube. Presently he straightened, peeled off and detached the suit, handed it carefully into the crowd. He stood waiting, clad in loincloth and some tight fabric over his feet, a crysknife in his right hand.
Jessica saw the girl-child Chani helping Paul, saw her press a crysknife handle into his palm, saw him heft it, testing the weight and balance. And it came to Jessica that Paul had been trained in prana and bindu, the nerve and the fiber—that he had been taught fighting in a deadly school, his teachers men like Duncan Idaho and Gurney Halleck, men who were legends in their own lifetimes. The boy knew the devious ways of the Bene Gesserit and he looked supple and confident.
But he's only fifteen , she thought. And he has no shield. I must stop this. Somehow, there must be a way to . . . She looked up, saw Stilgar watching her.
"You cannot stop it," he said. "You must not speak."
She put a hand over her mouth, thinking: I've planted fear in Jamis' mind. It'll slow him some . . . perhaps. If I could only pray—truly pray .
Paul stood alone now just into the ring, clad in the fighting trunks he'd worn under his stillsuit. He held a crysknife in his right hand; his feet were bare against the sand-gritted rock. Idaho had warned him time and again: "When in doubt of your surface, bare feet are best ." And there were Chani's words of instruction still in the front of his consciousness: "Jamis turns to the right with his knife after a parry. It's a habit in him we've all seen. And he'll aim for the eyes to catch a blink in which to slash you. And he can fight either hand; look out for a knife shift ."
But strongest in Paul so that he felt it with his entire body was training and the instinctual reaction mechanism that had been hammered into him day after day, hour after hour on the practice floor.
Gurney Halleck's words were there to remember: "The good knife fighter thinks on point and blade and shearing-guard simultaneously. The point can also cut; the blade can also stab; the shearing-guard can also trap your opponent's blade ."
Paul glanced at the crysknife. There was no shearing-guard; only the slim round ring of the handle with its raised lips to protect the hand. And even so, he realized that he did not know the breaking tension of this blade, did not even know if it could be broken.
Jamis began sidling to the right along the edge of the ring opposite Paul.
Paul crouched, realizing then that he had no shield, but was trained to fighting with its subtle field around him, trained to react on defense with utmost speed while his attack would be timed to the controlled slowness necessary for penetrating the enemy's shield. In spite of constant warning from his trainers not to depend on the shield's mindless blunting of attack speed, he knew that shield-awareness was part of him.
Jamis called out in ritual challenge: "May thy knife chip and shatter!"