From the essay/review by David Bordwell:
Early sound cartoons are sometimes characterized as “prisoners of the beat” because they create cycles of motion that are lined up with the musical meter. Lea traces how Disney animation became more fluid and flexible, syncing more around sound events than around rigid beats. She illustrates her case with analyses of Hell’s Bells (1929), The Three Little Pigs (1933), and Playful Pluto (1934). The last two are widely regarded as classic Silly Symphonies, and she sheds fresh light on them through the sort of micro-analysis brought to bear on Ivan.
Bordwell's verdict?She shows how sections gain a fast or slow tempo through the interaction of many factors, of which shot length is only one. In particular, Disney directors could change pace through a tool that Eisenstein didn’t have: altering the frame rate of animation. Normal animation is “on twos”; each drawn frame is photographed twice, to last for two film frames. Many stretches of the Disney cartoons are on twos, but sometimes, to create vivid sync points, the filmmakers go “on ones,” allotting one frame for each drawing. This is more expensive and time-consuming, but it allows for the sort of fine control of pace that we find in The Three Little Pigs. There the Wolf launches into “a jazzy, up-tempo gallop” that accelerates the danger bearing down on the pigs. In a similar way, Playful Pluto creates variety by “matching movement to different fractions of the beat and establishing differential rates of movement within the shot.” Imagineering, for sure.
Film Rhythm after Sound is a breakthrough in showing how narrative cinema masters time in its finest grain. We’re used to talking about scenes, shots, and lines of dialogue. Lea has taken us into the nano-worlds of a film: frames and parts of frames, fractions of seconds, phonemes. As Richard Feynman once said of atomic particles, “There’s plenty of room at the bottom.” Of course Lea doesn’t overlook characterization, plot dynamics, themes, and other familiar furniture of criticism. But she shows how our moment-by-moment experience depends on the sensuous particulars that escape our notice as the movie whisks past us. We can’t detect these micro-stylistics on the fly. Yet they are there, working on us, powerfully engaging our senses. Film criticism, informed by historical research, seldom attains this book’s level of delicacy. Analyzing a movie’s soundtrack will not be the same again.