How we cite our quotes: (Chapter.Paragraph)
Quote #4
"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." (16.145)
Kynes notes another fun fact of ecology. Blood is an important energy resource for us to consume, but since we also have blood in us, our bodies also provide an important energy resource. It's one of those circle of life things. A blood-drenched circle of life.
Quote #5
[Paul's] voice lowered and he repeated: "A poison—so subtle, so insidious… so irreversible. It won't even kill you unless you stop taking it. We can't leave Arrakis unless we take part of Arrakis with us." (22.147)
For a zoo to be successful, its habitats must replicate the animals' environments. This is because the animals' bodies have adjusted to a certain environment, and they need that environment to survive. Humans are the same way, only our habitat is planet-sized.
Quote #6
Jessica felt that the night was dominated by degrees of smallness in substances beneath their feet and hands—boulders or pea gravel or flaked rock or pea sand or sand itself or grit or dust or gossamer powder. (27.80)
There's an urban legend that Inuit think about snow more than other peoples because they have more words for "snow." It's been largely debunked now (source), but the idea has spread through our culture like the Slender Man meme. Herbert taps into something like the Inuit legend here to show that Jessica's thoughts are being shaped by Arrakis's environment.