You have to find the tone of the piece and modulate that. There are ways to indicate that - I try to incorporate the biggest range I can within the story, going from humorous to serious without it being jarring. That's the hardest part, to keep that balance. It requires being constantly aware of where you are in the story. You can't really do that in a movie: You can't slightly modulate the tone by the way the character's eyeballs look in one certain scene.