Paul Dano and Daniel Day-Lewis in There Will Be Blood Melinda Sue Gordon/Courtesy of Paramount Vantage

"When you discover Plainview at the beginning, he's almost learning himself how to do it. Anyone can swing an axe or a sledge. They kind of just made it up as they went along. Before cable rotary drilling became common use, they began by scooping this muck as it erupted out of the earth, scooping it up in saucepans and buckets. And then someone had the bright idea of trying to set up an A-frame and plunge the equivalent of a telegraph pole down into the ground. It was incredibly primitive. As the story progresses, then, there is something to learn about because the drilling procedure is a fairly complicated thing. But at the beginning it's just sheer blood and sweat," Day-Lewis says.

As Anderson began piecing his film together, it became clear that his minimal use of dialogue and vast open spaces would put a big burden on the score. Much of the energy and the pacing of the film would come from its music, so Anderson decided that a traditional composer might not be the most effective choice. Instead, he turned to Jonny Greenwood, guitarist for Radiohead, a British rock band known for its experimentation.

"[Greenwood] had a couple of pieces that existed before, that he had written for orchestra," Anderson says. "But he has written a few orchestral pieces I had heard that I thought were terrific. He also did an experimental film called Bodysong that he did the score for. I gave him a copy of the movie and then about three weeks later he came back with about two hours of music. I have no idea of how or when he did it, but he did it. It is kind of amazing. I cannot say that I did any real guiding or had any real contribution to it, except just to take what he gave us and find the right places for it."

Day-Lewis also found himself awestruck by Greenwood, in particular his self-taught technique: "The funniest thing about Johnny is that he didn't study composition. He studied violin, and then he went into the band, and the band became his life, but somehow along the way he taught himself composition. And he is the resident composer for the BBC Symphony Orchestra. [He] played a lot of the music, and scored the whole thing himself. I don't know how he did that."

But perhaps the film's greatest revelation is Dillon Freasier, who makes his film debut as H.W., Plainview's "son" and partner. When one of his workers is killed in a mining accident, Plainview decides to raise the man's boy as his own, and the pair travel around California in a Ford Model T, encouraging farmers and ranchers to sell their oil-rich properties at bargain-basement rates. During negotiations, Plainview exploits the boy's innocent looks to curry favor with women and Christian families. But when H.W. loses his hearing in an oil derrick explosion, Plainview is not emotionally equipped to deal with a handicapped child and partner.

"We did start out in Los Angeles and New York," says Anderson of the struggle to find an actor suited to the role, "reading young men with headshots, and that kind of thing, and resumes, and we thought that they should be sent to their rooms. We thought we needed a boy from Texas who knew how to shoot shotguns and live in that world. Casting director Cassandra Kulukundis asked around at the schools. She said: 'I am looking for a man in a young boy's body.' And one principal said: 'I have just the boy.' And it was Dillon."

Anderson didn't have Freasier read scenes, but simply talked with him about the part and says, "It was pretty clear that he was a very special young man. He took to it really well." Freasier, who had never been on a movie set or even seen a movie camera, reportedly loved the experience, and costar Day-Lewis says they immediately connected.

"I felt very close to Dillon, very fond of him," the veteran actor says. "He's a cowboy. His father is a rancher. Dillon has got his rodeo buckles. He's won numerous events. He does the round-ups. He's the real thing, and so he has this strange maturity that's very unusual."

According to Day-Lewis, Freasier had an insatiable curiosity for everything that happened on set, constantly absorbing new information "with such excitement and vision." But, adds Anderson, when it came to those scenes where he was expected to vent his physical frustration, he needed just a little push of encouragement — and a helping hand from mom.

"He had to struggle with Ciaran [Hinds] and he had to slap Daniel. He didn't like to do it initially," Anderson says of instructing Freasier to hit Day-Lewis across the face as hard as possible. The director recalls that it was only when Freasier's mother said, "You'd better do it, Dillon. They told you to do it. You can do it. It's okay," that the newly minted actor mustered the willpower to strike.

"His mom just raised him so beautifully and very respectfully," Day-Lewis says. "[She] is a state trooper and she wanted to do things right. And thought [that] she'd better check out this bunch that were going to be taking care of her son. So she went and got Gangs of New York. She was absolutely appalled. She thought she was releasing her child into the hands of this monster, and so there was a flurry of phone calls, and so somebody sent a copy of The Age of Innocence to her. Apparently," he laughs, "that did the trick."