Ryan Reynolds nervous singing in his new film

The 38-year-old actor plays fictional serial killer Jerry Hickfang in the black comedy and when he was told by director Marjane Satrapi he would have to show off his vocal skills he broke into a cold sweat, in the same way he would if required to have the internal medical examination.

In an interview with Shortlist magazine, he revealed: "Marjane would laugh at me with her weird expression, saying I looked like 'cold yoghurt' as I walked in to record my part. I had a flop sweat, I was desperately pale - it looked like I was going in for a very aggressive prostate exam."

Ryan - who is married to actress Blake Lively, with whom he has a baby daughter - didn't feel any more confident when he had to dance as his character, because he finds it so tough to follow choreography.

He explained: "I can't follow choreography. It's like I have a significant head injury when people start trying to tell me where to step or how to do it. But the singing terrified me the most. My co-stars happen to be Anna Kendrick, Gemma Arterton and Ella Smith - all fully trained singers, I was just doing a really bad Michael McDonald impression."