When one of the ambulances becomes stuck in the mud, the two sergeants refuse to assist in the effort to dislodge it and instead try to strike out on their own. Henry orders them to halt, and when they continue walking, Henry fires, wounding one; the ambulance driver Bonello uses Henry's pistol to finish the job. The group abandons all three ambulances and sets out on foot.
Chapter XXIX features one of the story's most dramatic and significant turning points, in Lieutenant Henry's shooting the deserting Italian sergeant. This is the first time, in this war novel, that the protagonist has fired a shot (using the pistol bought with Catherine Barkley on their last night together). And yet he fires the gun at a member of his own side rather than at an enemy. The irony will intensify in the next chapter, as Henry himself stands on the verge of being shot for desertion. The discipline of the front is replaced by a ragged retreat, and now the situation verges on complete disorder.
Again Hemingway emphasizes the difference between this war and those of myth and legend. The ambulance driver Piani suggests that the cavalry will appear, to which Henry replies "I don't think they've got any cavalry." Note in particular that the mud introduced in the first chapter of the novel has returned as a kind of antagonist here: It is responsible for the disabling of the ambulances, which in turn leads to the death of the deserting officer.
And yet the story is no less exciting for its lack of old-time heroics. Hemingway increases the tension in this chapter by telling us that enemy planes have passed overhead en route to bombing the road where the column of retreat is moving, and later in the chapter, Henry thinks he hears firing in the distance.
Imola town in the Emilia-Romagna region of north Italy.