How is shakespeare tension through scene two?

This is an extremely dramatic scene and Shakespeare sets the stage for the bloody murder with the "owl that shriek'd, the fatal bellman," as even nature cries out against the murder of Duncan. Lady Macbeth fears that the murder is unaccomplished, yet when Macbeth enters, he says, "I have done the deed." Suspense is heightened here by the quick exchange of dialogue between husband and wife:

"Did you not speak?"

"When?"

"Now."

"As I descended?"