The British actor plays US FBI officer Melvin Purvis in the 1930s gangster film and in preparing for his role kept a strong southern US accent throughout filming.
The film's director, Michael Bay, said: "Melvin Purvis was really a southern gentleman. So Christian kept the accent for 24 hours a day. It freaked out his young daughter. She said: 'Daddy doesn't talk like that!' he replied: 'Well, ah'm sorry, mah dear, but daddy's studying for a part, and ah'll be speaking like this for the next four months.' "
Michael also revealed that Johnny Depp - who plays the film's leading character, outlaw John Dillinger - was more influenced by wardrobe, and one of the most exciting parts of the production was when they got some clothes which actually belonged to the gangster.
Michael added: "We got to see some of Dilinger's packed suitcases, which he had left behind after an escape, and Johnny was able to actually hold his shirts in his hands. They still had the pink paper band around them from the Chinese laundry. And there were more accoutrements than you'd have thought for a guy on the run - shaving kit, talcum powder."
"You bet there's magic to that stuff. I'm not superstitious, but I couldn't help it," he added.
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