When adjusted properly, the flattened ends of the straw will vibrate as air flows over them. The vibration is passed on to the column of air inside the straw. This is just like the double reed on some woodwind instruments. The vibrating reed produces the oboe-like sound in the straw based on the length of the straw. By cutting off pieces of the straw, you alter the length of the air column and thus change the pitch. The English horn, oboe, and bassoon all use this same principle of vibration to make sound. These instruments, however, change the length of the column of air with holes, stops, and pads. Scissors are impractical.