Paul Berlin and Cacciato are fishing together, shortly after the events of the last chapter. Cacciato complains that there are no fish to catch. Berlin warns Cacciato that he’s spending too much time fishing—if he’s not careful, he’ll catch cold, at least according to Doc Peret.
In the Bible, fishing is a symbol of the process of Christian conversion. Thus, Cacciato’s complaint that there are no fish to catch might suggest his sense that the “souls” of the men around him have been lost to evil.
Suddenly, Berlin produces a grenade and tells Cacciato that the soldiers want Cacciato to touch it. Cacciato seems to understand what Berlin is saying, but doesn’t touch the grenade. Instead, he focuses on fishing. Berlin brings the grenade to Cacciato’s hand, forcing him to touch it. Then, as Cacciato continues to fish, Berlin walks back to the other soldiers and hands Oscar the grenade. Berlin explains that Cacciato touched the grenade, but that he’s too busy fishing to focus on anything—his mind is “a million miles away.” Oscar nods and says, “That’s everyone.”
Cacciato clearly doesn’t know what he’s assenting to by touching the grenade, and yet his touch is enough for Johnson and for Berlin. The illusion of group unity is so important to Johnson in his plot to kill Martin that he doesn’t care that it’s just an illusion—he doesn’t care that Cacciato doesn’t really give assent. We now begin to understand why the soldiers wanted to hunt down Cacciato in the first place: they couldn’t let the man who knew about their murder escape.