In John Scalzi's novel "Old Man's War," the phrase "Christ on a popsicle stick" serves as an expression of surprise or disbelief. This creative analogy captures a moment of shock, illustrating how characters react to unexpected situations in the story. The use of such vivid, imaginative phrases highlights Scalzi's unique writing style and his ability to blend humor with serious themes.

The novel revolves around themes of aging, technology, and humanity as it follows the protagonist who joins the Colonial Defense Forces at an advanced age. The narrative combines elements of science fiction with philosophical questions, making the phrase a fitting reflection of the surprising and often absurd challenges faced by characters in an expansive universe.