Chloë Grace Moretz's head was superimposed on a body double in 'If I Stay'.

The young actress struggled to learn the cello for her new movie role so producers used computer trickery to place her head on a double to film the instrument scenes.

She explained: ''I tried to learn a cello for seven months, but then I realised it's much harder than any other instrument and I couldn't learn it. So then they cut my head off and put it on to another girl's body. So I did scenes where my hands are by my side and I was playing cello with my head.''

And despite her jet-setting movie career, the 17-year-old star admits she has a serious phobia of planes and recently had a panic attack while travelling from New York to Los Angeles.

Chloë told 'Chelsea Lately': ''I have a terrible phobia of flying where I have straight up panic attacks. I thought for sure the plane was going down, I was like, 'I'm dying, this is it!'

''On the tour for my movie, I was in three cities in one day so I've been on a lot of planes but I still haven't [got over it].''