It's not enough anymore for an actor to just turn up on set and pretend to be someone else for a bit. Nowadays, it's all about undergoing a massive lifestyle change to showcase how dedicated you are to the craft.
In Cillian Murphy's case, he was asked to give up 15 years of vegetarianism for his starring role as gang leader Tommy Shelby on Peaky Blinders.
Talking to Mr Porter, the 40-year old admitted: 'I was vegetarian for about 15 years. But it was never a moral decision. It was more that I was worried about getting mad cow disease.
'For the first series of Peaky Blinders, they were anxious that I shouldn't look like a skinny Irish fella, and my trainer recommended meat.'
Needless to say it worked. The actor cuts a far bulkier figure than in his previous roles in Batman Begins and 28 Days Later.
Peaky Blinders is set to return for its fourth series later this year, with star turns from Tom Hardy and Adrien Brody. Check out everything we know so far below: