Director Juan José Campanella was not happy with the english translation of the title. The original title was intentionally ambiguous, since the spanish word "sus" could mean "their", but also "his" or "her".
When Pablo Sandoval explains the "passions" of the main characters, in the pub scene, he compares Irene with Susanita in her bride-to-be mania. Susanita is a character in the famous Argentinian comic-strip Mafalda, by Quino. Susanita is a blonde elementary school girl who is known for always talking about her future handsome husband and her future beautiful wedding, when she is not gossiping about the neighbor's marriages.
Spanish actor Javier Godino who plays the murderer in this film shares the surname with a well-known Argentine serial killer of the early 20th century: Cayetano Santos Godino also known by the nickname El Petiso Orejudo (The little "Big Ears"). This historical character is mentioned by Irene at the beginning of the movie.
The trivia items below may give away important plot points.
When Benjamín Esposito and Irene Menéndez Hastings go to confront the evil governmental officer who has released the assassin, the officer boasts about his powers and the differences between Benjamín and Irene recalling their last names: Irene is a Hastings (her cousins are "feudal lords" in the remote province of Jujuy) and Benjamín is a Esposito. Esposito in Italian means "orphan". In Spanish the word "expósito", which has almost the same sound as Esposito, also means "orphan", however the synonym "huerfano" is far more common in use, making the reference somewhat obscure yet not imperceptible (the etymology is the same as the word "exposed" and refers to how orphans would be abandoned, left exposed to the element), so the comment on the name is a complex trans-cultural and ethnic dismissing.
The soccer team seen scoring a goal in the stadium scene is called Racing Club. Guillermo Francella, who plays Pablo Sandoval in the movie, is a huge fan of theirs. Director Juan José Campanella is also a fan of Racing. Eduardo Sacheri, one of the writers and author of the novel on which this movie is based, prefers their rivals, Independiente.
When the notary at the bar is explaining that the names found in the letters from Isidoro Gómez are all soccer players from Racing Club, Pablo Sandoval asks him is he still considers Racing Club his passion even though 9 years has passed since the last time Racing Club won a championship. Racing Club spent actually 35 years without winning a championship after the one mentioned in the movie.