pbr The Prince of Wales and the Duchess of Cornwall came across an unusual performance of the song Somewhere Over The Rainbow earlier.br ppbr It was staged by sound sculptor Henry Dagg on his ''cat organ'' which consisted of a row of 16 squeaky toy catsbr ppbr The performance had the Royal couple reduced to tears of laughter.br ppbr TV gardener Alan Titchmarsh, actor Brian Blessed and musician Jools Holland were among the celebrities at the new green festival in the grounds of Clarence House, the prince's official residence.