Snowden
Snowden is a member of Yossarian's flight during a mission, and acts as catalyst for the fundamental change in Yossarian's mentality and outlook. After their plane takes heavy anti-aircraft fire, Snowden is mortally wounded and it is Yossarian who attempts to come to Snowden's aid by treating a serious leg wound with white bandages and sulfanilamide powder.
Eventually Yossarian notices bleeding from Snowden's armpit and realises that he has another wound below his flak suit. As Yossarian rips open the flak suit, a fatal wound beneath exposes Snowden's internal organs which fall out onto the floor. A huge chunk of flak had ripped straight through his ribs from behind. Yossarian is horrified at the sight. Snowden is about to die, but is still just able to tell Yossarian he is cold. Yossarian covers Snowden in a parachute, and comforts him by saying "there, there".
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."
Read more about this topic: Yossarian, Biographical Summary, Actions in "Catch-22"