The bathroom scene took 2 days to shoot. For 12 hours a day, Mark Wahlberg rested his bare bottom on a cold toilet, Garrett Hedlund stood in a hot shower, and Tyrese Gibson wore nothing but a robe. Mark Wahlberg had to be helped off the toilet at the end of each day, and Garrett Hedlund's skin peeled and pruned.
Ethan Hawke, Matt Damon and Ben Affleck all turned down the part of Bobby. The part eventually went to Mark Wahlberg. Ethan Hawke loved the script but could not commit to it because of scheduling conflicts. Matt Damon and Ben Affleck both said no because they found the script to be "ultra-violent".
Mark Wahlberg plays a character named Bobby Mercer. There was a baseball player named Bobby Murcer who famously played for the New York Yankees during parts of the 60's, 70's and 80's. Wahlberg is a fan of the Boston Red Sox, the rival team of the Yankees.
This is the second movie in which Mark Wahlberg portrays a character whose name is a derivative of Robert. The first is The Perfect Storm (2000), in which he portrayed Bobby Shatford; the third being Shooter (2007), in which he portrayed Bob Lee Swagger.
The trivia items below may give away important plot points.
In the first draft of the screenplay none of the brothers die. In the second draft Jack is killed. The screenwriters thought that it would add more of an intense dislike for Victor Sweet and a more emotional state of the rest of the brothers.
The music playing in the background when Green confronts Fowler at Sweet's bar is "Smiling Faces" by Motown band The Undisputed Truth. It's a song about being wary of two-faced people, as trusting them will only lead to betrayal.