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

Or . . . And Paul hesitated . . . the girdle was more than it seemed .
The Harkonnen appeared too confident against a man who'd this day led the forces of victory against Sardaukar legions.
Feyd-Rautha noted the hesitation, said: "Why prolong the inevitable? You but keep me from exercising my rights over this ball of dirt."
If it's a flip-dart , Paul thought, it's a cunning one. The girdle shows no signs of tampering .
"Why don't you speak?" Feyd-Rautha demanded.
Paul resumed his probing circle, allowing himself a cold smile at the tone of unease in Feyd-Rautha's voice, evidence that the pressure of silence was building.
"You smile, eh?" Feyd-Rautha asked. And he leaped in mid-sentence.
Expecting the slight hesitation, Paul almost failed to evade the downflash of blade, felt its tip scratch his left arm. He silenced the sudden pain there, his mind flooded with realization that the earlier hesitation had been a trick—an overfeint. Here was more of an opponent than he had expected. There would be tricks within tricks within tricks.
"Your own Thufir Hawat taught me some of my skills," Feyd-Rautha said. "He gave me first blood. Too bad the old fool didn't live to see it."
And Paul recalled that Idaho had once said, "Expect only what happens in the fight. That way you'll never be surprised ."
Again the two circled each other, crouched, cautious.
Paul saw the return of elation to his opponent, wondered at it. Did a scratch signify that much to the man? Unless there were poison on the blade! But how could there be? His own men had handled the weapon, snooped it before passing it. They were too well trained to miss an obvious thing like that.
"That woman you were talking to over there," Feyd-Rautha said. "The little one. Is she something special to you? A pet perhaps? Will she deserve my special attentions?"
Paul remained silent, probing with his inner senses, examining the blood from the wound, finding a trace of soporific from the Emperor's blade. He realigned his own metabolism to match this threat and change the molecules of the soporific, but he felt a thrill of doubt. They'd been prepared with soporific on a blade. A soporific. Nothing to alert a poison snooper, but strong enough to slow the muscles it touched. His enemies had their own plans within plans, their own stacked treacheries.
Again Feyd-Rautha leaped, stabbing.
Paul, the smile frozen on his face, feinted with slowness as though inhibited by the drug and at the last instant dodged to meet the downflashing arm on the crysknife's point.
Feyd-Rautha ducked sideways and was out and away, his blade shifted to his left hand, and the measure of him that only a slight paleness of jaw betrayed the acid pain where Paul had cut him.
Let him know his own moment of doubt , Paul thought. Let him suspect poison .
"Treachery!" Feyd-Rautha shouted. "He's poisoned me! I do feel poison in my arm!"
Paul dropped his cloak of silence, said: "Only a little acid to counter the soporific on the Emperor's blade."
Feyd-Rautha matched Paul's cold smile, lifted blade in left hand for a mock salute. His eyes glared rage behind the knife.
Paul shifted his crysknife to his left hand, matching his opponent. Again, they circled, probing.
Feyd-Rautha began closing the space between them, edging in, knife held high, anger showing itself in squint of eye and set of jaw. He feinted right and under, and they were pressed against each other, knife hands gripped, straining.
Paul, cautious of Feyd-Rautha's right hip where he suspected a poison flip-dart, forced the turn to the right. He almost failed to see the needlepoint flick out beneath the belt line. A shift and a giving in Feyd-Rautha's motion warned him. The tiny point missed Paul's flesh by the barest fraction.
On the left hip!
Treachery within treachery within treachery , Paul reminded himself. Using Bene Gesserit-trained muscles, he sagged to catch a reflex in Feyd-Rautha, but the necessity of avoiding the tiny point jutting from his opponent's hip threw Paul off just enough that he missed his footing and found himself thrown hard to the floor, Feyd-Rautha on top.
"You see it there on my hip?" Feyd-Rautha whispered. "Your death, fool." And he began twisting himself around, forcing the poisoned needle closer and closer. "It'll stop your muscles and my knife will finish you. There'll be never a trace left to detect!"
Paul strained, hearing the silent screams in his mind, his cell-stamped ancestors demanding that he use the secret word to slow Feyd-Rautha, to save himself.
"I will not say it!" Paul gasped.
Feyd-Rautha gaped at him, caught in the merest fraction of hesitation. It was enough for Paul to find the weakness of balance in one of his opponent's leg muscles, and their positions were reversed. Feyd-Rautha lay partly underneath with right hip high, unable to turn because of the tiny needlepoint caught against the floor beneath him.
Paul twisted his left hand free, aided by the lubrication of blood from his arm, thrust once hard up underneath Feyd-Rautha's jaw. The point slid home into the brain. Feyd-Rautha jerked and sagged back, still held partly on his side by the needle imbedded in the floor.
Breathing deeply to restore his calm, Paul pushed himself away and got to his feet. He stood over the body, knife in hand, raised his eyes with deliberate slowness to look across the room at the Emperor.
"Majesty," Paul said, "your force is reduced by one more. Shall we now shed sham and pretense? Shall we now discuss what must be? Your daughter wed to me and the way opened for an Atreides to sit on the throne."
The Emperor turned, looked at Count Fenring. The Count met his stare—gray eyes against green. The thought lay there clearly between them, their association so long that understanding could be achieved with a glance.