Dueling Movies: With No Country for Old Men, which was being shot around the same time in rural Texas, note One story notes how close both sets were, to the point where during filming of the oil derrick scene, Old Men had to shut down filming for the day due to the smoke interrupting the shoot. was also a Darker and Edgier film by (a) respected auteur(s), released around the same time by the same distributors (Paramount Vantage & Miramax) and competed for Best Picture at The Oscars.
Daniel Day-Lewis, naturally, went to town. He hit Paul Dano earlier than the intended mark during the scene where Daniel screams at Eli to heal his son. The look of shock when Eli tumbles to the ground is genuine. His hatred of Eli, which he continued even off-camera, led Paul Dano to confess he thought he would actually die during some points of the filming.
During the baptism scene, Paul Dano is actually smacking Daniel Day-Lewis around, bringing it around full-circle.
The Other Marty: Kel O'Neill, the original actor for Eli left halfway through production due to being intimidated by Daniel Day-Lewis during the original filming of the bowling alley scene.
Playing Their Own Twin: Paul Dano, originally cast as Paul Sunday, took the larger role of Eli Sunday (making the brothers twins) after Kel O'Neill departed the production.