Bandoneon player and composer Juan Pablo Jofre rehearses his Four Tangos Bandoneon Concerto with the Symphony Silicon Valley. (See the wikipedia entry for Juan Pablo Jofre and his bio at his website.)
The bandoneon is a concertina-like instrument that may remind you of the accordion — though it is played by means of buttons rather than the familiar accordion keyboard. You might be surprised to see such an instrument playing with a symphony orchestra. It is not a regular member of such orchestras, but composers have been increasingly interested in writing for the instrument, with notable compositions by Astor Piazzola.