When you do bigger jobs there's more attention and when you film in New York you get loads of paparazzi everywhere. It affects your work because you're trying to think about the person you're acting with and you've got 20 other lenses taking pictures of you at the same time, and it throws you.

The thinnest I've ever been was after I had my appendix out, during the London run of The Seagull. I went down to 112 pounds and realized my brain doesn't work when I'm that thin, so I can't do my job. That's why, when I came out here, I never had that whole Hollywood pressure thing. I never said I wanted to be a lead actress; I never said I wanted to be a film actress. This need to trump everyone bewilders me. I'm only 25. I'm not better than anyone. I just want to watch other people and learn to be good.

On film sets I can see everyone, and I really still find that so difficult.

I am committed to helping Alzheimer's Society in any way I can. My family and I rely on the help of organisations like Alzheimer's Society to help us understand the disease and guide us in the care of my grandmother. It's been a privilege to meet so many people with dementia.

Leonardo is the most incredible actor, on the planet, with a couple of people alongside him. Getting to act with him is just [amazing]. I walked away from my audition for that and I couldn't believe that I'd been acting with him. I've worked with amazing people, but my friends freak out that I'm working with him. I freak out in a geeky acting way. They freak out in a starstruck way. He's Leonardo DiCaprio, and his fame is so big. That's a complete tangent about that.

People get married when they're 18 and spend their whole lives together. I think their greatest fear is that someone will see it as a fling because they were young and it didn't mean anything.

It's actually easier to play a leading role than it is to play a supporting role.