The trivia item below may give away important plot points.
The movie contains several references to Ernest Hemingway's The Sun Also Rises. Most obviously, Oyelowo grabs a copy of the book when quickly packing to leave the St Regis hotel room. Also, Theron's character discards a framed photo of Edgerton's character participating at the running of the bulls in San Fermin (made famous by the novel). Further, the movie's plot generally relates to the novel's in that it follows an American man's journey in a Spanish-speaking country. Finally, though more of a reference to Hemingway generally, Oyelowo's character opens a "Harry's Bar," a reference to the real life Manhattan and Venice bar that Hemingway often frequented and wrote about.