How do Eckels and Travis respond to the challenge of the hunt in Ray Bradbury's "A Sound of Thunder"?

Eckels and his guide react in markedly different ways when the Tyrannosaurus Rex steps out of the jungle and approaches them: Eckels is terrified and cannot shoot, but Travis reacts quickly and bravely fires at the advancing "Tyrant Lizard," killing it.

This reaction is certainly foreshadowed when Eckels initially reports to the Time Safari, Inc. office. There the clerk warns Eckels of the danger and affords him the opportunity to cancel his trip: 

Anything happens to you,...

Eckels and his guide react in markedly different ways when the Tyrannosaurus Rex steps out of the jungle and approaches them: Eckels is terrified and cannot shoot, but Travis reacts quickly and bravely fires at the advancing "Tyrant Lizard," killing it.

This reaction is certainly foreshadowed when Eckels initially reports to the Time Safari, Inc. office. There the clerk warns Eckels of the danger and affords him the opportunity to cancel his trip: 

Anything happens to you, we're not responsible. Those dinosaurs are hungry." 
Eckels flushed angrily. "Trying to scare me!" 
Frankly, yes. We don't want anyone going who'll panic at the first shot....Your personal check's still there. Tear it up."
Mr. Eckels looked at the check. His fingers twitched.

When the mammoth creature explodes onto the scene, Eckels does, indeed, panic. For, when he sees this monster shaking the earth and approaching, Eckels, cries, "Get me out of here." He tells Travis and Lesperance that on his previous safaris he had good guides and safe conditions.  

"This time, I figured wrong. I've met my  match and admit it. This is too much for me to get hold of." 

Travis hisses at him to be quiet, and he instructs Eckels to turn around slowly and return to the Machine. When Eckels moves, the Tyrant Lizard sees him and charges. The two guides bravely fire into the eyes in which they see themselves mirrored. Then, "like a stone idol, like a mountain avalanche, Tyannosaurus crashes to the earth. 

The pusillanimous Eckels cowers in the ship on the return to the travel company, knowing that were it not for the courage and skill of Travis and Lesperance, he would have been eaten by the Tyrannosaurus Rex.