When Michael and Fredo are having their drinks in Havana, Michael tells Fredo about the plot to assassinate him. Fredo asks, "Who?" Michael replies "Roth." But he has a look (and sound) of disgust when he says, "Rrrrothhhh," as if he's reproaching himself for having fallen for Roth's promises about Havana--and nearly getting himself and Kay killed as a result.