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

It's one of Duke Leto's fighting men we took on Arrakis! Feyd-Rautha thought. No simple gladiator this! A chill ran through him, and he wondered if Hawat had another plan for this arena—a feint within a feint within a feint. And only the slavemaster prepared to take the blame!
Feyd-Rautha's chief handler spoke at his ear: "I like not the look on that one, m'Lord. Let me set a barb or two in his knife arm to try him."
"I'll set my own barbs," Feyd-Rautha said. He took a pair of the long, hooked shafts from the handler, hefted them, testing the balance. These barbs, too, were supposed to be drugged—but not this time, and the chief handler might die because of that. But it was all part of the plan.
"You'll come out of this a hero ," Hawat had said. "Killed your gladiator man to man and in spite of treachery. The slavemaster will be executed and your man will step into his spot ."
Feyd-Rautha advanced another five paces into the arena, playing out the moment, studying the slave. Already, he knew, the experts in the stands above him were aware that something was wrong. The gladiator had the correct skin color for a drugged man, but he stood his ground and did not tremble. The aficionados would be whispering among themselves now: "See how he stands. He should be agitated—attacking or retreating. See how he conserves his strength, how he waits. He should not wait."
Feyd-Rautha felt his own excitement kindle. Let there be treachery in Hawat's mind , he thought. I can handle this slave. And it's my long knife that carries the poison this time, not the short one. Even Hawat doesn't know that .
"Hai, Harkonnen!" the slave called. "Are you prepared to die?"
Deathly stillness gripped the arena. Slaves did not issue the challenge!
Now, Feyd-Rautha had a clear view of the gladiator's eyes, saw the cold ferocity of despair in them. He marked the way the man stood, loose and ready, muscles prepared for victory. The slave grapevine had carried Hawat's message to this one: "You'll get a true chance to kill the na-Baron ." That much of the scheme was as they'd planned it, then.
A tight smile crossed Feyd-Rautha's mouth. He lifted the barbs, seeing success for his plans in the way the gladiator stood.
"Hai! Hai!" the slave challenged, and crept forward two steps.
No one in the galleries can mistake it now , Feyd-Rautha thought.
This slave should have been partly crippled by drug-induced terror. Every movement should have betrayed his inner knowledge that there was no hope for him—he could not win. He should have been filled with the stories of the poisons the na-Baron chose for the blade in his white-gloved hand. The na-Baron never gave quick death; he delighted in demonstrating rare poisons, could stand in the arena pointing out interesting side effects on a writhing victim. There was fear in the slave, yes—but not terror.
Feyd-Rautha lifted the barbs high, nodded in an almost-greeting.
The gladiator pounced.
His feint and defensive counter were as good as any Feyd-Rautha had ever seen. A timed side blow missed by the barest fraction from severing the tendons of the na-Baron's left leg.
Feyd-Rautha danced away, leaving a barbed shaft in the slave's right forearm, the hooks completely buried in flesh where the man could not withdraw them without ripping tendons.
A concerted gasp lifted from the galleries.
The sound filled Feyd-Rautha with elation.
He knew now what his uncle was experiencing, sitting up there with the Fenrings, the observers from the Imperial Court , beside him. There could be no interference with this fight. The forms must be observed in front of witnesses. And the Baron would interpret the events in the arena only one way—threat to himself.
The slave backed, holding knife in teeth and lashing the barbed shaft to his arm with the pennant. "I do not feel your needle!" he shouted. Again he crept forward, knife ready, left side presented, his body bent backward to give it the greatest surface of protection from the half-shield.
That action, too, didn't escape the galleries. Sharp cries came from the family boxes. Feyd-Rautha's handlers were calling out to ask if he needed them.
He waved them back to the pru-door.