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: Writing a novelty song about Italians doing the mambo--that takes a lot of determination, talent and hard work.