Gleeson explains that he feels that acting should be a draining process. He says, “As an actor, you should feel like you’re wrestling the material, like it’s using up your energy and your resources. You should be drained by the process. I think the key is not to be comfortable.”
As an Irish actor, Gleeson had to work on his natural accent to ensure it didn’t creep into his portrayal of the character. His main technique was to use poetry to practice Milne’s voice. He explains, “I would recite poems with my dialogue coach to help practice my voice.” Gleeson used Milne’s accent from waking up to going to bed, believing this would help him portray Milne’s PTSD. He explains, “Portraying PTSD onscreen terrified me. I didn’t want it to come across as a melodramatic thing. I wanted it to feel contained and real.”
(via)