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What is spice in ‘Dune,’ and why does it turn characters’ eyes blue?

Things are about to get spicy.
/ Source: TODAY

You could wear blue-colored contacts, or — if you happen to be a character in "Dune," the movies based on Frank Herbert's sci-fi books — you could ingest some spice. They'd have the same effect.

"Dune: Part Two" follows Paul Atreides' (Timothée Chalamet) transformation from occupying duke to one of the Fremen, the indigenous population of the planet Arrakis.

Part of his transformation is physical: After spending enough time in the desert, Paul and his mother, Lady Jessica (Rebecca Ferguson), earn the striking blue eyes of the rest of the Fremen.

Here's what to know about spice, and why it leads to piercing blue eyes.

Javier Bardem as Stilgar in Warner Bros. Pictures and Legendary Pictures’ action adventure “DUNE: PART TWO.”
A spicy stare from Javier Bardem in "Dune: Part Two."Warner Bros.

Why do ‘Dune’ characters’ eyes turn blue?

The blue eyes are a side-effect of consuming vast amounts of spice. The Fremen are surrounded by spice in the desert of Arrakis, and so their eyes are blue.

"Those are called the eyes of Ibad," Leo Wiggins, co-host of the "Dune" podcast "Gom Jabbar," tells TODAY.com. "That’s the characteristic ‘blue within blue eyes’ of the Fremen because inevitably their diets are very filled with spice."

OK, then. What is spice?

Spice, also called melange, is an ingredient found only on the planet Arrakis, and is "the driving force for the galactic economy," the hosts of "Gom Jabbar" say in their spice-centric episode.

The family that rules Arrakis controls the spice trade. House Atreides occupied Arrakis before House Harkonnen invaded.

"Spice is both wealth and power," the podcast hosts say.

How is spice made?

We can thank sandworms, those gigantic desert creatures, for spice. Spice is "a byproduct of a sandworm's life cycle," the "Gom Jabbar" hosts said in their episode. "No worms, no spice."

Spice is generated during a worm's larval phase, when water combines with excretion in their nest. Over time, and with exposure to the sun, that mixture becomes spice.

Mining is also involved in spice production, as "Dune: Part Two" shows. Spice harvesters scrape spice from the surface of the sand. Then, it's processed to create the powder used throughout the empire.

What does spice do?

Spice is powerful because it affects, and expands, perception. It leads to powers of precognition in some people.

Spice is also extremely expensive for most. But the Fremen of Arrakis have a unique proximity to vast quantities of spice, incorporating it into their clothes, rugs and food. This has side effects of its own.

"If you’re surrounded by spice and you consume it a lot, you get health benefits. You’re immune to most diseases, your aging slows down. You live three to four times the average human,” Wiggins tells TODAY.com.

Why is spice important for the world of 'Dune'?

The Spacing Guild relies on spice to explore the universe. Spice's expanded powers of perception make it possible for navigators to travel safely.

"Thousands of years ago, (the Spacing Guild) realized they could train their ship navigators to use spice to use their prescience to fly ships safely at faster than light speed so they're not crashing into suns, or each other. This gave the guild a near-complete monopoly on faster-than-light space travel," the "Gom Jabbar" hosts said on their podcasts.

"The empire itself is only possible because of the guild, the spice and the travel that it allows."

Dune
Zendaya as Chani in "Dune: Part Two." Note the eyes.Warner Bros.

The Bene Gesserit, a powerful sisterhood, use spice to access their psychic powers.

Their leaders undergo a potentially fatal process called the agony, seen in "Dune: Part Two," in which they ingest the Water of Life, another worm byproduct.

If they survive, they become Reverend Mothers, inheriting the memories of all the women who have come before them. "They rely on spice to continue minting new Reverend Mothers," the podcast episode said.

In the world of "Dune," don't follow the money: Follow the spice.