How does the author use foreshadowing in The Sirens of Titan?

In the section titled, A Deserter in Time of War, Rumfoord fills the gap in Constant's memory for the reader, but Constant is still seemingly unaware that the story Rumfoord tells him is about himself. Rumfoord lets slip a remark that the Martian Army is about to be the first ever to die for a good cause. The remark catches Boaz's attention, but he does not know what to make of it. This remark serves to foreshadow the intentionally disastrous invasion scheme.