Quoth Wiki:
Snowden's death embodies Yossarian's desire to evade death; by seeing Snowden's entrails spilling over the plane, he feels that "Man was matter, that was Snowden's secret. Drop him out a window and he'll fall. Set fire to him and he'll burn. Bury him and he'll rot, like other kinds of garbage. The spirit gone, man is garbage."
The experience on the plane dramatically changes Yossarian's attitude towards life. He now looks only to protect his own life and, to a lesser extent, the lives of his close friends. Yossarian also turns against the military after this flight and refuses to wear a uniform. His justification is that he simply "doesn't want to," perhaps because he was traumatized and depressed by Snowden's death. The excuse Captain Korn gives to General Dreedle is that Snowden died in one uniform, and his remains were soaked into Yossarian's, and all of Yossarian's other articles of clothing were in the laundry. General Dreedle says "That sounds like a lot of crap to me." Yossarian replies, "It is a lot of crap, sir."
Another Analysis:
Snowden’s death has been hinted at throughout the novel, but it is only in the second-to-last chapter that we are finally allowed to see the scene from beginning to end. Because it is placed near the end of the novel and is so clearly an important event, Snowden’s death functions as the technical climax of Catch-22, even though it took place before many of the novel’s other events. The progression of the scene of Snowden’s death is similar to Yossarian’s progression throughout the novel: at first, Yossarian thinks that he has control over death and that he can stop Snowden’s leg wound from bleeding and save Snowden’s life; later, he finds that death is a force utterly outside his control. The “secret” revealed to him here is that man is made of inanimate matter and that no human hands can restore life to a body once it has been destroyed by flak, disease, or drowning.
Yossarian has taken Snowden’s secret to heart, and he realizes that the impulse to live is the most important human quality. But the impulse to live is not simply a desire to survive at any cost: Yossarian cannot live as a hypocrite or as a slave; as a result, he decides to incur enormous personal danger by attempting to escape from the military rather than take the safe deal that would betray his friends. Yossarian chooses simply to take his life back into his own hands, openly rejecting (rather than, as the deal would have required, falsely embracing) the mentality of Catch-22 and making his run for freedom. He is inspired in this decision by the rather absurd example of Orr, who has escaped to Sweden.
