Double clarinet

This instrument is from Lebanon. Its bamboo reeds are cut from the instrument's body. A loop of string adjusts each reed so it will vibrate when the player blows in the end. The two clarinets are fastened together with string and beeswax.

Placing your fingers on different holes changes the amount of air vibrating in the tube, which makes different notes.

How do you play an instrument that has twelve fingerholes?