Actors are always worried about their lines: How many, what inflection, what word to emphasize, picking up cues. But in film, it's not the lines that we care about, it's the transitions, the reaction shots, the moments before and after the lines. The important moments in film are all BETWEEN the lines - that's what draws us in, that's what creates suspense. Will he cry or won't she? Will he just sit there, or will he erupt? Will she say "yes," or will she say "no?" And great actors know exactly how long to milk these heightened silences. Lines? Sure, learn them, but it's how interesting you are in those silences that count – especially on camera.