How does Margaret Atwood use imagery in Oryx and Crake?

Imagery:

"He feels like weeping. Then he hears a voice - his own! - saying boohoo; he sees it, as if it's a printed word in a comic-strip balloon. Water leaks down his face."

"He jumps out of reach, watches while the pigoon slithers back down, then launches itself again. Its eyes gleam in the half-light; he has the impression it's grinning."