Continuuophone, ætherphone, etherphone, thereminophone, termenvox, and thereminvox are early names for the electronic musical instrument, the theramin. The device's final name is named after its inventor, the Soviet inventor Léon Theremin, who patented the device in 1928.
The theremin is played without physically touching the instrument. There are two antennae, which sense the relative position of the hand, with one hand controlling the frequency of the sound produced by the theremin, and the other hand controlling the volume.
Marty McFly played the device, first by using his hands like he was playing a guitar, to the bewilderment of onlookers. He then began to dance, first by imitating the "chicken dance" he witnessed Biff Tannen perform, while under the influence of the Citizen Plus treatment, in the alternate 1986 where Emmett Brown and Edna Strickland controlled Hill Valley as First and Second Citizen Brown.
Marty then danced the moonwalk. Cue Ball Donnely was impressed, and attempted to move his feet the way that he had seen Marty do. When Marty left the booth, Cue Ball entered the booth to try out the continuuophone himself.