Jodorowsky's Dune Uncovered
Scene 101-104 : Sandworm Attack
Paul and Jessica's damaged 'thopter comes out of the cyclone and lands in the desert.
They jump away, taking their possessions with them, and behind them a worm eats the 'thopter.
After sheltering among the rocks, they set off towards some cultivated vegetation, with Paul planting a thumper to distract a nearby worm.
As the worm destroys the thumper Paul & Jessica cross sand-drums, their footsteps resounding across the desert, attracting the worm.
They just manage to climb into the safety of rocks as the worm reaches them, its mouth in front of them, searching.
Suddenly another thumper rings out, drawing the worm away, and, relieved, they climb higher, using some man-made steps cut into the rocks, which opens into a ravine.
While there aren't any publically available Moebius storyboards for this section there are some from the Lynch movie that mirror this scene.