At the showâ€™s Television Criticsâ€™ Association press tour panel, Ruffalo said that the character of Thomas has a mental illness which means has has to take â€œstabilizers and antipsychoticsâ€ which cause him to put on weight. Ruffalo shot the scenes where he played the other twin, Dominic, before putting on the pounds over a five-week period of force feeding.
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â€œWhen youâ€™re force feeding yourself some of the romance of food leaves,â€ Ruffalo said. â€œThose five weeks were kind of lonely, Iâ€™d been a way from my family and (Thomas) hears voices, and I wasÂ imaging that life and there was a couple weeks where I was just staying by myself, going down into the heart of this mental illness and studying it.â€
â€œI Know This Much Is Trueâ€ follows the parallel lives of the twin brothers in a story of betrayal, sacrifice, and forgiveness, taking place against the backdrop of 20th century America. The series is based on the book of the same name by Wally Lamb, and Ruffalo said he felt a lot of pressure taking on both roles and the mental illness part of Dominicâ€™s character in particular.
â€œThereâ€™s an element of mental illness in this project and you want to be as honest as you can to that, and it means a lot to me to be honest to that which means going into that world and getting to know it and getting comfortable with it,â€ Ruffalo said. â€œI was really afraid to play it, I think itâ€™s a really an important issue and I want to tell it as honestly as possible, the responsibility of playing it was really apparent to me.â€
In terms of the difference between the two brothers, Ruffalo said that Dominic is much more â€œbound to our ideas of manhood and masculinity,â€ while Thomas is more â€œsensitive and openâ€ because he relates more with his mother.
As executive producer, writer and director Derek Cianfrance put it, the brothers â€œhave the same DNA, but they 40 years of completely different life experiences.â€
Cianfrance said that another actor played both twins when Ruffalo was in the opposite role, and that he shot the series â€œvery simply,â€ shot-counter shot, in order to not have in order to avoid the technical challenges overwhelming the story and the characters.
In terms of inspiration for the series, Cianfrance pointed to the famous dinner scene between Robert De Niro and Al Pacino in Michael Mannâ€™s â€œHeat.â€
â€œTheyâ€™re never on screen togetherâ€¦.(Mann) was creating flip sides of the coin, you canâ€™t see the head and the tail together,â€ he said.
The series also stars Melissa Leo, Rosie Oâ€™Donnell, Archie Panjabi, Imogen Poots, Juliette Lewis, and Kathryn Hahn.
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