Teenage actor Daniel Radcliffe ruined his first on-screen sex scene - he couldn't stop giggling. The Harry Potter star, 18, stars in the forthcoming film December Boys - but admits he struggled to take the steamy scene with co-star Teresa Palmer seriously. He says, "It's very, very hard to stop giggling I found. I suppose the thing I was worried about was, 'Am I going to get an erection? Is this going to be really sexy? Is this going to be a bit awkward?' "But when you get in there, it's not sexy in the slightest."