Seth Rogen's method punch to Amber

Seth Rogen punched Amber Heard in the face "to get her in the mood" for their movie. US actor Seth Rogen arrives at the premiere of the film 'Pineapple Express' at the Mann Village Theatre' in Los Angeles, California, USA, 31 July 2008. The film tells the story of a stoner and his dealer who are forced to go on the run from the police after the pothead witnesses a cop commit a murder. EPA/NINA PROMMER

US actor Seth Rogen arrives at the premiere of the film 'Pineapple Express' at the Mann Village Theatre' in Los Angeles, California, USA, 31 July 2008. The film tells the story of a stoner and his dealer who are forced to go on the run from the police after the pothead witnesses a cop commit a murder. EPA/NINA PROMMERThe pair co-star in forthcoming film 'The Pineapple Express' and Seth revealed they used violence as a way of bonding on set.He said: "We did hurt ourselves when we were filming it. James Franco cracked his face open, Danny McBride cracked the back of his head open, I punched Amber in the face just to get her in the mood for things, 'Welcome to the set, Amber.' Smack!"But it was a lot of fun. It's bonding to come and beat the c**p out of each other, you're very physical and you're in these somewhat homoerotic positions."Seth also revealed that the actors used a herbal cannabis substitute in the film, with some of the cast enjoying it more than others.He added to Britain's Guardian newspaper: "It's this s**t called Wizard Smoke, it's like non-alcoholic weed. I didn't like it. James didn't have that hard a time with it, but he will smoke anything. One thing about this guy, if you put it in front of him, he'll smoke it."