The tongues on this instrument can be plucked like those of a kalimba or mbira. But these tongues are actually short lengths of piezo film, normally used as vibration sensors or contact pickups. This is an unusual usage for the piezos: rather than being attached to some other vibrating body, here the piezos are themselves being played directly. When you pluck them, they generate the electronic signal that goes to the amplifier. The overhanging lengths of the piezos roughly determine their pitches. With their quick, percussive sound they cover a range from low to high, but they are not tuned to specific pitches.