Whistling

Whistling is a cool trick anyone can learn with enough patience. All you need to do is continuously blow whilst trying to produce any kind of noise. If nothing happens, try adjusting either your tongue's position, or the force behind your blows. In the beginning I was only able to produce sounds whilst inhaling. From there I learned how to whistle normally, and over time I've become quite proficient in controlling my whistles. At a certain level of mastery, you'll be able to whistle whilst inhaling just as proficiently as if you were exhaling. At that point, you will be ready for the infinite whistle.

Up until now, whistling has been restricted by your lung capacity. But now, once you learn how to whistle whilst inhaling, you'll never run out of oxygen. Thus you could theoretically whistle for a very long time.