Davros' right hand

By the time of the creation of the Daleks, Davros only had the use of his right hand, which he used to operate controls on his chair. These could perform functions for controlling doors, the Mark III travel machines, or his own life support system. (TV: Genesis of the Daleks)

On Necros, Bostock fired a gun which destroyed most of his right hand and with it his ability to operate independently. (TV: Revelation of the Daleks) For a short time after, his hand was replaced with a claw (COMIC: Emperor of the Daleks!) and finally with a prosthetic substitute. (AUDIO: The Juggernauts, TV: The Stolen Earth, Journey's End, The Magician's Apprentice, The Witch's Familiar) He was capable of projecting electric shocks from both his organic and mechanical hands, allowing him to ward off attackers. (AUDIO: Davros, TV: Revelation of the Daleks, Journey's End)

Within the Crucible, Davros used his artificial hand to shock the Meta-Crisis Tenth Doctor when he attempted to use a Z-Neutrino Biological Inversion Catalyser on him, which would have destroyed the Daleks. Soon after, Davros shocked Donna Noble when she picked up the weapon. However, by doing so, Davros inadvertently "spark[ed]" Donna's synapses following her exposure to the metacrisis, thus awakening her newfound Time Lord side which proved crucial in defeating the New Dalek Empire. (TV: Journey's End)