Eckels internal conflict in The Sound of Thunder is fear. He is terrified at what could happen to him on the time safari, but he goes anyway.
Eckels is intrigued by the idea of the real time machine that he sees at Time Safaris, he wants to go, but he wants a guarantee that he will be in one piece when he returns. After they arrive, he becomes terribly panicked and struggles with his fear, until he finally says:
"`Get me out of here,' said Eckels. `It was never like this before. I was always sure I'd come through alive. I had good guides, good safaris, and safety. This time, I figured wrong. I've met my match and admit it. This is too much for me to get hold of.' " (Bradbury)