Trapping a whim...

He strode to a beat,
Without drums around;
His mind did repeat,
A distinct periodic sound.

A ditty was soon afloat,
On his lips, and out,
It wasn't like what he wrote,
But had a charming clout.

He continued to walk along,
Losing himself to the tune,
Till he wished to jot down
                                 the song,
For that parade in June.

He sat down to id the notes,
But a page couldn't trap a whim,
He had whistled the tune away,
And it was now lost on him.