I was wondering how the guy whistles in this youtube video: Home - Edward Sharpe and The Magnetic Zeros Acoustic Cover (Jorge & Alexa Narvaez). He does some crazy no lip whistle. Googling "whistle without lips" led me to this little bit of info.

How to whistle with your mouth:

This whistle may require some practice and exercise because it takes strength in your tongue, jaw, and other parts of the mouth.
Draw your lips and the corners of your mouth as far back as you can. Your bottom teeth should not be visible, but it is okay if your top teeth show.
Pull the tongue taut and draw it back.
Broaden and flatten the tip of the tongue.
- Be sure there is a space between your teeth and tongue.
- Your tongue should float in your mouth more or less at the level of your bottom row of teeth.
Blow air gently out.
Direct your breath downwards towards your lower teeth. You should be able to feel the downward force of the air on your tongue.
- The sound is created by the tongue working with the upper teeth to force air over the surface of the tongue and into the lower teeth.
Experiment with the position of your tongue, cheek muscles, jaw, and anything else for a wide variety of whistle sounds.