sentence1: But you have to admire Merrill's  Any old Alley opportunist can write a novelty Italian song (That's Amore) or a novelty mambo song (Papa Loves Mambo), but to write a novelty song about Italians doing the mambo--that takes 
sentence2: To write a novetly song about Italians doing the mambo-- that takes something else, but you have to admire Merrill's Any old Alley opportunist can write a novelty Italian song (That's Amore) or a novelty mambo song (Papa Loves Mambo).