"was once" - This phrase supports the element of plot, specifically the event of the train derailment.
"rarely lets himself admit fear" - This phrase supports the element of characterization, specifically Enrique's personality trait of not admitting fear.
"The Train of Death" - This phrase supports the element of setting, specifically the nickname given to the train.
The purpose of the author's use of these phrases and techniques is to create a vivid and engaging narrative, as well as to provide information about the plot, characters, and setting. By using descriptive language and details, the author helps to bring the story to life and create a sense of realism and tension for the reader.