Dakota Johnson was thinking about her neighbours having sex when she landed the lead role in 'Fifty Shades of Grey'.

The 24-year-old actress had been recalling watching her neighbours' bedroom antics just before receiving a call informing her she would be playing Anastasia Steele in the film adaptation of E.L. James' erotic novel.

Dakota told Entertainment Weekly magazine: ''The phone rang and I remember looking out of this apartment to an apartment across the street. And I was looking at all of these people in their windows. And I thought, 'How funny would it be if I were watching people having sex right now?'''

Dakota's character, the virginal Anastasia, is a college student who is seduced by sadomasochistic billionaire Christian Grey (Jamie Dornan) - claims she was speechless when she received the offer as she has worked hard for the coveted role.

She recalled: ''They said, 'You got the offer!' and I couldn't speak. I was just so relieved. I was crying and crying. Water was literally squirting out of my eyes because I had been so stressed out, and there's this giant Doberman Pincher lying on the bed next to me. And he just slowly fell asleep. It was so special and [this dog] didn't give a f**k about me and what I was going through.''

Dakota was announced to play Anastasia in September following months of speculation as to who would land the role, while Jamie was later confirmed as Christian as a replacement for Charlie Hunnam, who quit the project.