It can be a challenge for some sound-making machines to be understood via video. Sometimes there’s no way to truly understand how it’s working without the experience of playing it. The theremin, patented in 1928 and played above by its Russian inventor Léon Theremin, is one such instrument.
The controlling section usually consists of two metal antennas which sense the position of the player’s hands and control oscillators for frequency with one hand, and amplitude (volume) with the other, so it can be played without being touched. The electric signals from the theremin are amplified and sent to a loudspeaker.
Still fascinating to watch, however, especially when played by the inventor. This video, and many others are featured in io9’s The Oddest-Looking Musical Instruments on Earth. And/or there are more inventions and instruments in the archives.