Not a common sight
Someone (not for the first time) observed yesterday that Triple P "must be happy" as he was whistling. This is an odd assertion. Triple P whistles because we are recalling a tune. Our mental state has nothing to do with it.
Triple P has always whistled tunes, a habit he picked up from his mother. Even now we sometimes comes across a piece of music we recognise as a tune Triple P's mother used to whistle years ago. However, Triple P, as we started to think about it, realised that we hardly ever hear anyone else whistling a tune. This is particular true of girls although this may be partly explained by the fact that there used to be an old wives tale in England that "a whistling woman never marries".
In fact, people have intimated to Triple P that whistling is a lost habit which was much more common fifty years ago. Mike Oldfield once said that he composes much of his musc whilst walking and whistling, which may explain the strong melodic lines in much of his music; you would be hard pushed to whistle Harrison Birtwistle (!).
The apotheosis of musical whistling, as far as Triple P is concerned has to be Roger Whittaker who had a TV show which Triple P remembers from when he was a child. We still don't know quite how he produced the sounds he did in his single Mexican Whistler!