I was lucky enough to interview Roger many years back and see him do this live. He was raised in Africa and learned very early in life to do this. Instead of blowing to whistle he would breath in to whistle. He explained it to me, but to this day I can't do it! Enjoy!<iframe width="420" height="315" src="//www.youtube.com/embed/xaPoBhiMkgs?rel=0" frameborder="0" allowfullscreen></iframe>