Sam Rockwell think you've ''got to have some levity'' when working on a heavy topic.

The 49-year-old actor stars alongside Frances McDormand, Woody Harrelson and Peter Dinklage in the new dark comedy movie by Martin Mcdonagh 'Three Billboards Outside Ebbing, Missouri', which tackles the tale of the kidnapping and murder of a teenage girl.

However, despite the heavy topic, Rockwell admitted he likes to keep the mood on set light and said he always needs to ''have some laughs'' when he's filming.

Speaking to The Hollywood Reporter, Rockwell said: ''I think when you're doing a heavy topic, you've got to have some laughs, don't you think? I mean, you've got to have some levity in between. It's too heavy for 12, 14 hours. I go home and watch 'The Simpsons' or something.''

The film follows months after the murder of teenager Angela (Kathryn Newton) and there is still no culprit so her mother Mildred Hayes (McDormand) makes a bold move by painting three signs leading into the town with controversial messages directed at police chief William Willoughby (Harrelson).

When Willoughby's second-in-command Officer Jason Dixon (Rockwell) gets involved, the battle is only exacerbated.

Newton, 20, also admitted she felt the pressure to be at the top of her game because of who her castmates were.

Speaking previously to BANG Showbiz in October, she said: ''I'm a huge fan of everybody in the movie. I love all of them so when you get to be in a movie you're like, 'OK I better not mess up.' That's how I acted. I couldn't pass this opportunity I would have done anything.''

'Game of Thrones' star Dinklage also revealed that he knew that the script was going to be fantastic.

He said: ''It's Martin McDonagh. I knew when I read the script it was one of the best scripts I've ever read.''