of little use on Arrakis. In Children of Dune it is noted that a weapon has been developed on Arrakis called a "pseudo-shield". This device will attract and enrage any nearby sandworm, which will destroy anything in its vicinity. The Fremen manage to develop a unique relationship with the sandworms. They learn to avoid most worm attacks by mimicking the motions of desert animals, moving with the natural sounds of the desert rather than rhythmic vibrations. However, they also develop a device known as a thumper with the express purpose of generating a rhythmic vibration to attract a sandworm. This can be used either as a diversion or to summon a worm to ride. The Fremen have secretly mastered a way to ride sandworms across the desert. First, a worm is lured by the vibrations of a thumper device. When it surfaces, the lead worm-rider runs alongside it and snares one of its ring-segments with a special "maker hook". The hook is used to pry open the segment, exposing the soft inner tissue to the abrasive sand. To avoid irritation, the worm will rotate its body so the exposed flesh faces upwards, lifting the rider with it. Other Fremen may then plant additional hooks for steering, or act as "beaters", hitting the worm's tail to make it increase speed. A worm can be ridden for several hundred kilometers and for about half a day, at which point it will become exhausted and sit on the open desert until the hooks are released, whereupon it will burrow back down to rest. Worm-riding is used as a coming-of-age ritual among the Fremen, and Paul's riding and controlling a giant sandworm cements him as a Fremen leader. Paul also uses worms for troop transport into the city during the Battle of Arrakeen after using atomic weapons to blow a hole in the Shield Wall. After the reign of Leto II, sandworms become un-rideable. The one exception is a young girl named Sheeana, an Atreides descendant who possesses a unique ability to control the worms and safely move around them. Fremen also use the sharp teeth of dead sandworms to produce the sacred knives they call crysknives. Approximately long, these hand-to-hand weapons are either "fixed" or "unfixed". An unfixed knife requires proximity to a human body's electrical field to prevent its eventual disintegration, while fixed knives are treated for storage. Fremen tradition dictates that