Drum sand

Drum sand was a surface feature of some dunes, a crystalline formation which caused them to amplify the footsteps of a traveller, attracting the attention of worms. It is also powdery and causes a traveller to sink into it, further increasing the danger. This is what happens to Ishanti in Sisterhood of Dune when she distracts a worm that is about to devour Griffin Harkonnen.