Yossarian refers to Snowden's guts as his "secret." They were hidden inside his flak suit, though pierced by flak, until Yossarian ripped open the suit and out they come. Yossarian "reads" Snowden's secret in his intestines. This alludes to an ancient Roman practice of reading prophecies in the intestines of sacrificed animals. If man has been dehumanized by the war, then Snowden is essentially made an animal in his death. Not to mention that he has been sacrificed for some supposed greater cause. As for prophecies, let's look at what Yossarian reads in his guts: man is mortal. Significantly, this event may spark much of Yossarian's paranoia about death – to start. Its retribution, however, (and this may be why the scene is at the end of the novel), could be that Yossarian uses it as a way to overcome his paranoia. By some sort of absurd logic, knowing that you have to die and will die might mean you can stop worrying about it.