The idea of hyperlink cinema wasn't something Mexican director Alejandro Gonzalez Inarritu created, but he was one of the best practitioners of this story-telling method. He used it in his first three films, telling the story of a group of characters, whose links were only revealed to the audience later in the story. Clearly sensing that the fad is over, he moved away from the technique in his recent movies, including the 2014 Best Picture Oscar nominee Birdman.

Inarritu has always been a critical darling. Every one of his movies has at least one Oscar nomination on its resume, and most are for their performances. 21 Grams, his first English-language and second overall movie, garnered two well-deserved Oscar nominations for 2003. However, one could argue that its third star also deserved a nomination.

The three main characters in 21 Grams are Paul Rivers (Sean Penn), who needs a heart transplant or he will die; Christina Peck (Naomi Watts), who is left in emotional shambles after her husband and two daughters are killed in a car accident; and Jack Jordan (Benicio Del Toro), an ex-convict who is now a born-again Christian.

At first, they seem like people from three very different worlds, which is always a key in movies like these. However, they are linked by the car crash that kills Christina's family. It turns out that Jack was behind the wheel of the truck that killed them. When Christina's husband dies, she agrees to donate his heart and it goes to Paul, of course. But it's not just enough to have a central event that links them together.

The script, written by Guillermo Arriaga, also has to bring them together. Paul is the force that does that. Without Paul's drive to find the truth behind the events that lead him to receiving a heart, 21 Grams never goes anywhere.

21 Grams is more like a puzzle than, say, Syriana, Crash or Traffic, mostly because it is non-linear. Even Inarritu's next film, Babel, unfolds mostly in chronological order, although Inarritu worked with a much larger canvas.

21 Grams' mystery isn't in the story, but it's in the way it is told. The opening shot shows Christina and Paul in bed, but we soon discover that they are both married to other people. How do we reach the point where they sleep together? That's the introductory mystery of 21 Grams, even as the story continues to unfold.

What also keeps 21 Grams engaging is its performances. For a director so interested in breaking down the walls of conventional storytelling, Inarritu has an unbelievable talent when it comes to bringing out great performances from his stars. Naomi Watts is at full command, swinging from loving mother to grief-stricken widow with surprising ease. She is put through an emotional wringer during the film's two hours. She is an actress willing to completely break down and trusts Inarritu to bring out her best. Obviously she enjoyed working with him, since she gives a delightful performance in Birdman.

The men in this movie are also quite good. Benicio Del Toro, who was nominated for Best Supporting Actor, gives a heart-breaking, tormented performance as Jack. Seeing him completely lose faith in his religion is one of the more shocking scenes in the film.

Sean Penn, who was not nominated for Best Actor but still won for Clint Eastwood's Mystic River that year, plays the film's heart, which sounds a bit odd. After all, he spends part of the movie without a heart that works. But he's the one that pulls the trio together. Inarritu calls him the film's guardian angel in the little featurette included on the DVD and that's an apt description of Penn's character. That burden requires Penn to give a more nuanced, delicate performance, very different from what's asked of him in the Eastwood film.

Inarritu also gets a few good supporting performances from Melissa Leo, who plays Jack's wife, and Charlotte Gainsbourg, who plays Paul's. Danny Huston appears briefly as Christina's husband.

Since Inarritu is on the cusp of possibly winning his first Oscar, it's important to look at the films that lead up to his decision to make Birdman. Sure, Birdman is a lighter movie on its surface, but it still has an emotional link to Inarritu's other, heavy dramas. 21 Grams may seem obsessed with death, especially with a title that references the amount of weight “lost” by the human soul when someone dies, but it is more about how our actions while we are alive define us. In 21 Grams, characters define themselves based on what they give each other and in Bridman, they define themselves by what they give to an audience. In other words, like all good filmmakers, Inarritu can try to step into other genres and lighten up, but he can't avoid his favorite themes.

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