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

Hawat by my side! the Baron thought. The Sardaukar will give him to me. If they suspect anything at all it's that I wish to destroy the Mentat. And this suspicion I'll confirm! The fools! One of the most formidable Mentats in all history, a Mentat trained to kill, and they'll toss him to me like some silly toy to be broken. I will show them what use can be made of such a toy .
The Baron reached beneath a drapery beside his suspensor bed, pressed a button to summon his older nephew, Rabban. He sat back, smiling.
And all the Atreides dead!
The stupid guard captain had been right, of course. Certainly, nothing survived in the path of a sandblast storm on Arrakis. Not an ornithopter . . . or its occupants. The woman and the boy were dead. The bribes in the right places, the unthinkable expenditure to bring overwhelming military force down onto one planet . . . all the sly reports tailored for the Emperor's ears alone, all the careful scheming were here at last coming to full fruition.
Power and fear—fear and power!
The Baron could see the path ahead of him. One day, a Harkonnen would be Emperor. Not himself, and no spawn of his loins. But a Harkonnen. Not this Rabban he'd summoned, of course. But Rabban's younger brother, young Feyd-Rautha. There was a sharpness to the boy that the Baron enjoyed . . . a ferocity.
A lovely boy , the Baron thought. A year or two more—say, by the time he's seventeen, I'll know for certain whether he's the tool that House Harkonnen requires to gain the throne .
"M'Lord Baron."
The man who stood outside the doorfield of the Baron's bedchamber was low built, gross of face and body, with the Harkonnen paternal line's narrow-set eyes and bulge of shoulders. There was yet some rigidity in his fat, but it was obvious to the eye that he'd come one day to the portable suspensors for carrying his excess weight.
A muscle-minded tank-brain , the Baron thought. No Mentat, my nephew . . . not a Piter de Vries, but perhaps something more precisely devised for the task at hand. If I give him freedom to do it, he'll grind over everything in his path. Oh, how he'll be hated here on Arrakis!
"My dear Rabban," the Baron said. He released the doorfield, but pointedly kept his body shield at full strength, knowing that the shimmer of it would be visible above the bedside glowglobe.
"You summoned me," Rabban said. He stepped into the room, flicked a glance past the air disturbance of the body shield, searched for a suspensor chair, found none.
"Stand closer where I can see you easily," the Baron said.
Rabban advanced another step, thinking that the damnable old man had deliberately removed all chairs, forcing a visitor to stand.
"The Atreides are dead," the Baron said. "The last of them. That's why I summoned you here to Arrakis. This planet is again yours."
Rabban blinked. "But I thought you were going to advance Piter de Vries to the—"
"Piter, too, is dead."
"Piter?"
"Piter."
The Baron reactivated the doorfield, blanked it against all energy penetration.
"You finally tired of him, eh?" Rabban asked.
His voice fell flat and lifeless in the energy-blanketed room.
"I will say a thing to you just this once," the Baron rumbled. "You insinuate that I obliterated Piter as one obliterates a trifle." He snapped fat fingers. "Just like that, eh? I am not so stupid, Nephew. I will take it unkindly if ever again you suggest by word or action that I am so stupid."
Fear showed in the squinting of Rabban's eyes. He knew within certain limits how far the old Baron would go against family. Seldom to the point of death unless there were outrageous profit or provocation in it. But family punishments could be painful.
"Forgive me, m'Lord Baron," Rabban said. He lowered his eyes as much to hide his own anger as to show subservience.
"You do not fool me, Rabban," the Baron said.
Rabban kept his eyes lowered, swallowed.
"I make a point," the Baron said. "Never obliterate a man unthinkingly, the way an entire fief might do it through some due process of law . Always do it for an overriding purpose—and know your purpose! "
Anger spoke in Rabban: "But you obliterated the traitor, Yueh! I saw his body being carried out as I arrived last night."
Rabban stared at his uncle, suddenly frightened by the sound of those words.
But the Baron smiled. "I'm very careful about dangerous weapons," he said. "Doctor Yueh was a traitor. He gave me the Duke." Strength poured into the Baron's voice. "I suborned a doctor of the Suk School ! The Inner School ! You hear, boy? But that's a wild sort of weapon to leave lying about. I didn't obliterate him casually."
"Does the Emperor know you suborned a Suk doctor?"