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

I'll give them a show such as they've never had before , Feyd-Rautha thought. No tame killing where they can sit back and admire the style. This'll be something to take them by the guts and twist them. When I'm Baron they'll remember this day and won't be a one of them can escape fear of me because of this day .
Feyd-Rautha gave ground slowly before the gladiator's crablike advance. Arena sand grated underfoot. He heard the slave's panting, smelled his own sweat and a faint odor of blood on the air.
Steadily, the na-Baron moved backward, turning to the right, his second barb ready. The slave danced sideways. Feyd-Rautha appeared to stumble, heard the scream from the galleries.
Again, the slave pounced.
Gods, what a fighting man! Feyd-Rautha thought as he leaped aside. Only youth's quickness saved him, but he left the second barb buried in the deltoid muscle of the slave's right arm.
Shrill cheers rained from the galleries.
They cheer me now , Feyd-Rautha thought. He heard the wildness in the voices just as Hawat had said he would. They'd never cheered a family fighter that way before. And he thought with an edge of grimness on a thing Hawat had told him: "It's easier to be terrified by an enemy you admire ."
Swiftly, Feyd-Rautha retreated to the center of the arena where all could see clearly. He drew his long blade, crouched and waited for the advancing slave.
The man took only the time to lash the second barb tight to his arm, then sped in pursuit.
Let the family see me do this thing , Feyd-Rautha thought. I am their enemy: let them think of me as they see me now .
He drew his short blade.
"I do not fear you, Harkonnen swine," the gladiator said. "Your tortures cannot hurt a dead man. I can be dead on my own blade before a handler lays finger to my flesh. And I'll have you dead beside me!"
Feyd-Rautha grinned, offered now the long blade, the one with the poison. "Try this one," he said, and feinted with the short blade in his other hand.
The slave shifted knife hands, turned inside both parry and feint to grapple the na-Baron's short blade—the one in the white gloved hand that tradition said should carry the poison.
"You will die, Harkonnen," the gladiator gasped.
They struggled sideways across the sand. Where Feyd-Rautha's shield met the slave's halfshield, a blue glow marked the contact. The air around them filled with ozone from the field.
"Die on your own poison!" the slave grated.
He began forcing the white-gloved hand inward, turning the blade he thought carried the poison.
Let them see this! Feyd-Rautha thought. He brought down the long blade, felt it clang uselessly against the barbed shaft lashed to the slave's arm.
Feyd-Rautha felt a moment of desperation. He had not thought the barbed shafts would be an advantage for the slave. But they gave the man another shield. And the strength of this gladiator! The short blade was being forced inward inexorably, and Feyd-Rautha focused on the fact that a man could also die on an unpoisoned blade.
"Scum!" Feyd-Rautha gasped.
At the key word, the gladiator's muscles obeyed with a momentary slackness. It was enough for Feyd-Rautha. He opened a space between them sufficient for the long blade. Its poisoned tip flicked out, drew a red line down the slave's chest. There was instant agony in the poison. The man disengaged himself, staggered backward.
Now, let my dear family watch , Feyd-Rautha thought. Let them think on this slave who tried to turn the knife he thought poisoned and use it against me. Let them wonder how a gladiator could come into this arena ready for such an attempt. And let them always be aware they cannot know for sure which of my hands carries the poison .
Feyd-Rautha stood in silence, watching the slowed motions of the slave. The man moved within a hesitation-awareness. There was an orthographic thing on his face now for every watcher to recognize. The death was written there. The slave knew it had been done to him and he knew how it had been done. The wrong blade had carried the poison.
"You!" the man moaned.
Feyd-Rautha drew back to give death its space. The paralyzing drug in the poison had yet to take full effect, but the man's slowness told of its advance.
The slave staggered forward as though drawn by a string—one dragging step at a time. Each step was the only step in his universe. He still clutched his knife, but its point wavered.
"One day . . . one . . . of us . . . will . . . get . . . you," he gasped.
A sad little moue contorted his mouth. He sat, sagged, then stiffened and rolled away from Feyd-Rautha, face down.
Feyd-Rautha advanced in the silent arena, put a toe under the gladiator and rolled him onto his back to give the galleries a clear view of the face when the poison began its twisting, wrenching work on the muscles. But the gladiator came over with his own knife, protruding from his breast.
In spite of frustration, there was for Feyd-Rautha a measure of admiration for the effort this slave had managed in overcoming the paralysis to do this thing to himself. With the admiration came the realization that here was truly a thing to fear.