Where do Lyman and Henry speak directly to each other in "The Red Convertible"? Where do they speak indirectly? How do they communicate without speech? How does Erdrich present the moments of emotion in this story?

A lot of the indirect communication between Henry and Lyman comes from Lyman's observations of Henry, including Henry's movements. For example, when they first drive places in their car, Lyman notices that Henry "was asleep with his arms thrown wide." Lyman knows that Henry is at complete peace. Later, when Henry returns from Vietnam, Lyman knows that he is not quite right because "he was never comfortable sitting still anywhere but always up and moving around." Henry's body movements imply that he is in a state of constant agitation. Even Henry's laugh seems more like a choking noise, and when Henry is watching TV, he bites through his lip, causing a stream of blood to go down his chin. It is through Henry's gestures and body movements that the brothers communicate indirectly, without speech.
They also communicate through speech and writing; for example, they write to each other when Lyman is serving in Vietnam. They often speak directly to each other about the car they share; for example, many of Lyman's letters to Henry in Vietnam are about the state of the car. 
The moments of emotion in the story are often expressed in a very subtle way. For example, the reader knows that Lyman is suffering greatly after Vietnam from seeing him bite through his lip and start to bleed when he is watching TV. The reader senses that Lyman is attempting to help his brother when Lyman destroys the car so that Henry can find it. When Lyman drowns at the end of the story, Henry expresses his pain by submerging his beloved car. Much of the emotion in the story is expressed through action rather than through dialogue or explanation.