I quote a whole lot here because I don't know what to leave out.
The banker says something boastful to Jessica and it moves Paul to confront him. Then the banker counters, but Paul stands firm. The banker becomes offended, and that offense is compounded when Kynes defends Paul. Then things almost get out of hand.
Is it merely that the others show him up? They break a certain expected decorum? Or maybe there's some sort of metaphor here, the banker comparing himself to the blood drinking birds, then Paul modifying that comparison to one of cannibals?
Also, why is the water magnate upset?
"I enjoy watching the flights of birds on Arrakis," the banker [a Guild Bank representative] said, directing his words at Jessica. "All of our birds, of course, are carrion-eaters, and many exist without water, having become blood-drinkers."
The stillsuit manufacturer's daughter, seated between Paul and his father at the other end of the table, twisted her pretty face into a frown, said: "Oh, Soo-Soo, you say the most disgusting things."
The banker smiled. "They call me Soo-Soo because I'm financial adviser to the Water Peddlers Union." And, as Jessica continued to look at him without comment, he added: "Because of the water-sellers' cry -- 'Soo-Soo Sook!'" And he imitated he call with such accuracy that many around the table laughed.
Jessica heard the boastful tone of voice, but noted most that the young woman had spoken on cue -- a set piece. She had produced the excuse for the banker to say what he had said. She glanced at Lingar Bewt. The water magnate was scowling, concentrating on his dinner. It came to Jessica that the banker had said: "I, too, control that ultimate source of power on Arrakis -- water."
Paul had marked the falseness in his dinner companion's voice, saw that his mother was following the conversation with Bene Gesserit intensity. On impulse, he decided to play the foil, draw the exchange out. He addressed himself to the banker.
"Do you mean, sir, that these birds are cannibals?"
"That's an odd question, young Master," the banker said. "I merely said the birds drink blood. It doesn't have to be the blood of their own kind, does it?"
"It was not an odd question," Paul said, and Jessica noted the brittle riposte quality of her training exposed in his voice. "Most educated people know that the worst potential competition for any young organism can come from its own kind." He deliberately forked a bite of food from his companion's plate, ate it. "They are eating from the same bowl. They have the same basic requirements."
The banker stiffened, scowled at the Duke.
"Do not make the error of considering my son a child," the Duke said. And he smiled.
Jessica glanced aroundt he table, noted that Bewt has brightened, that both Kynes and the smuggler, Tuek, were grinning.
"It's a rule of ecology," Kynes said, "that the young Master appears to understand quite well. The struggle between life elements is the struggle for the free energy of a system. Blood's an efficient energy source."
The banker put down his fork, spoke in an angry voice: "It's said that the Fremen scum drink the blood of their own dead."
Kynes shook his head, spoke in a lecturing tone: "Not the blood, sir. But all of a man's water, ultimately, belongs to his people -- to his tribe. It's a necessity when you live near the Great Flat. All water's precious there, and the human body is composed of some seventy per cent water by weight. A dead man, surely, no longer requires that water."
The banker put both hands against the table beside his plate, and Jessica thought he was going to push himself back, leave in a rage.
Kynes looked at Jessica. "Forgive me, my Lady, for elaborating on such an ugly subject at table, but you were being told falsehood and it needed clarifying."
"You've associated so long with Fremen that you've lost all sensibilities," the banker rasped.
Kynes looked at him calmly, studied the pale, trembling face. "Are you challenging me, sir?"
The banker froze. He swallowed, spoke stiffly: "Of course not. I'd not so insult our host and hostess."
Jessica heard the fear in the man's voice, saw it in his face, in his breathing, in the pulse of a vein at his temple. The man was terrified of Kynes!