How does Laura Hillenbrand use imagery in Unbroken: A World War II Story of Survival, Resilience, and Redemption?

Imagery:

"... it was absolutely dark and absolutely silent, save for the chattering of Phil's teeth. The ocean was a flat calm. A rough, rasping tremor ran through the men. The sharks were rubbing their backs along the raft bottoms."

"Louie began to come apart. At night, the Bird stalked his dreams, screeching, seething, his belt buckle flying at Louie's skull. In the dreams, the smothered rage in Louie would overwhelm him, and he'd find himself on top of his monster, his hands on the corporal's neck, strangling the life from him."