I have long been fascinated by the theremin, the first truly electronic instrument, and have used it as an example in my courses on electrodynamics because it uses the idea of mutual inductance and how circuits can be tuned to resonate at given frequencies.
The theremin is played without touching the instrument, the movement of one hand controlling the volume and the other hand controlling the pitch. By moving one’s hands, one changes the mutual inductance of the circuits and thus changes the resonance frequency. It is not an easy instrument to master.
Here is a nice demonstration of it, with Peter Pringle playing Over the Rainbow on a 1929 RCA theremin.