Kelly Reilly has revealed that she liked pretending to be a drug addict in Flight.
Director Robert Zemeckis admitted that the actress' overdose scene was one of the toughest parts to shoot because he couldn't bring himself to watch.
But Kelly admitted: "It's weird because I actually enjoyed the overdose scenes. I had to learn how to shoot up, I had no idea. Some actors have to learn how to play the guitar for a part but I had to learn how to do that.
"I wanted to make it look like she was making coffee, like she had done it a hundred times. I enjoyed getting into that world - it might sound dark - but it was something I had never done before. The heroin part was a small part of the movie for me, but I knew the way Robert was shooting it was very sensitive."
Kelly, who has appeared in Guy Ritchie's Sherlock Holmes films, was so committed to making sure her performance was realistic that she enlisted the help of a former drug addict on set.
"I needed somebody to tell me how to use needles," she said.
"We did five-minutes sequences of her shooting up, so I needed somebody to help me. This was someone who had been an addict 10 years ago but has recovered through NA (Narcotics Anonymous)."
She added: "He became someone who I had other questions for, and he generously shared his story to me and how he climbed out of it and what heroin did to me."
:: Flight opens in cinemas on February 1.