How did the dead body of Jim Conklin seem to mock the living?

The dying Jim looks like an exaggerated version or caricature of the living. Jim stiffens. His legs shake and his arms flail slightly. He stretches upward and then falls to the ground, dead. Henry watches this display in horror and sadness. He rushes up to Jim, whose mouth is frozen open, blue-lipped, in a smile. Henry turns towards the battlefield with rage, as if to deliver a speech. All he can say is "Hell" as the red sun sits on the horizon.