The Ladykillers

Mrs. Marva Munson, a strict, religious and elderly widow, meets "Professor" Goldthwaite Higginson Dorr, a southern linguist/Edgar Allan Poe enthusiast who expresses interest in the room she has for rent and asks to use her root cellar for rehearsals of an early music ensemble he directs, to which she agrees. The fellow musicians in the pretend ensemble are actually a gang of criminals. The band are composed of a dim football player named Lump as the "muscle", the overconfident movie effects technician Garth Pancake as the "jack of all trades" (who suffers from IBS), the crass and sloppy Gawain McSam as their "inside man", and the Vietnamese, tough-as-nails General as their "tunneling expert" (who hides his chain smoking from the disapproving Mrs. Munson by concealing his cigarette in his mouth). The group of criminals plan to dig a tunnel through the exposed wall in the cellar in order to break into the underground vault for a nearby riverboat casino. The dirt they remove is taken out at night and tossed off a bridge onto a garbage barge as it passes below.
A series of mishaps threaten to derail their plan, including "inside man" Gawain losing his janitorial job at the casino, Mrs. Munson's cat running off with Garth's finger when he accidentally sets a plastic explosive off in his hand, and a visit from the local sheriff. Nonetheless, the group manages to break through the wall of the vault and snatch the loot. Before the group can get away, Mrs. Munson uncovers the plot and tells Dorr to return the money and go with her to church on Sunday, or face the authorities. Dorr attempts to persuade her otherwise, by claiming that the casino's insurance company will replace the money, resulting in each shareholder only losing a single penny. He also claims he will donate a full share of the stolen funds to Bob Jones University, a Bible college which Mrs. Munson admires, but she insists on her judgment.
The gang decides they have no choice but to murder her. None of them are eager to kill an old woman so they draw straws. The task falls to Gawain but he fails to go through with it after he realizes Mrs. Munson reminds him of his mother. This starts a fight between Garth and Gawain which results in Gawain being fatally shot with his own gun; the group dumps his body off the bridge onto the trash barge. Garth then attempts to steal the entire sum of money and escape with his girlfriend, "Mountain Girl," but the General kills them both with a garotte wire and discards their bodies onto the barge. After drawing lots again, the General is about to kill Mrs. Munson in her sleep, concealing his cigarette in his mouth as per usual. He is suddenly startled by a clock, accidentally swallowing his cigarette. In a frenzied search for water, The General trips over Mrs. Munson's cat and falls down the stairs to his death. As Lump and Dorr dispose of The General's body onto the barge, Lump has a change of heart and tells Dorr he wants to do what Mrs. Munson says. When Dorr refuses, Lump attempts to shoot him with a revolver but the chamber is empty; he peers down the barrel and accidentally shoots himself with the round that was in the next chamber, falling off the bridge onto the barge. Dorr, now alone, pauses to admire a passing raven and recite poetry until the raven dislodges the head of a decaying grotesque on top of the bridge which knocks GH Dorr over the railing. As he tumbles off the bridge, his cape gets caught on the ironwork railing and hangs him to death, before it tears and he too finally falls onto the barge headed for garbage island.
Mrs. Munson finds all the money in her basement and believes that the criminals fled and decided to leave the money. She informs the police about the money but, believing her to be insane, they tell her to keep it; she decides to donate it to Bob Jones University. The film ends with Pickles dumping Garth's severed finger onto the barge. The credits start with Mrs. Munson's church singing.

Question: How did they originally decide who was going to kill the old lady, Mrs Munson?
Answer: Drawing straws