Complex sentence: The song is performed on the Salisbury Plain in the second Beatles film, "Help!" and, just as it finishes, a mine explodes, leading the audience to believe briefly that the Beatles have been blown up.
Split into simpler sentences: The song is performed on the Salisbury Plain in the second Beatles film, "Help!". In the film'Help!', just as the song finishes, a mine is exploded, leading the audience to believe, briefly, that the Beatles have been blown up.