Learning to Apparate is difficult, and students run the risk of "splinching"—being physically split between the origin and destination—which requires the assistance of the Ministry's Accidental Magic Reversal Squad to undo properly, although essence of dittany can also mend certain wounds. Splinching is quite common during lessons, and can be uncomfortable (and at times rather gruesome) depending on the body parts splinched, but is ultimately harmless if properly reversed. Although Ron can Apparate, he isn't terribly skilled at it, and splinches himself at least three times (once losing half an eyebrow, two fingernails and part of his arm). Harry and Hermione both pick up the skill quickly in comparison. As explained in the "Half-Blood Prince", there is no word spell to Apparate or Disapparate, but the caster has to concentrate on the location on which he has to apparate, needs to be fully focused on the spell, and also has to "feel" it through the whole body.