During an interview with The Telegraph, Alejandro González Iñárritu quoted from "On Myth", which was the beginning of the film, by the Mexican poet Jaime Sabines: 'Someone spoke to me all the days of my life, / into my ear, slowly, taking their time. / Said to me: live, live, live! / It was death'.
When Alejandro González-Iñárritu was casting the role of Ana at a school, Hanaa Bouchaib came up to him, grabbed him by the shirt and said: "Are you the one who's making the movie? I want in" The director said that he was so captivated that really keep her in mind.
The song that is heard in Tito's house while Marambra is dancing naked is "Como te extraño, mi amor", written by the Argentine Leo Dan and performed by the Mexican band Café Tacuba. Alejandro González Iñárritu is also from México.
The trivia item below may give away important plot points.
In almost every scene in the film, there is an object that shows the character's reflections. There are several key moments where Uxbal's reflection intentionally doesn't match up with his actual body movements, indicating that he is slightly removed from this reality.