The theremin is a slightly odd instrument, which doesn’t even need to be touched to be played. Here’s how it works: the theremin player stands in front of the instrument, while moving their hands around its two metal antennae. One antenna controls the pitch, while the other determines the volume. Then, electric signals from the theremin are amplified and the sound is projected through a loudspeaker.
In the video, the Da ensemble play on what sound like theremins, but are actually matryomins. Matryomins are one-antenna theremins, which are then inserted into a Matryoshika figure, AKA a Russian doll.