Brie Larson claims Armie Hammer and Cillian Murphy are ''obsessed'' with drawing penises.

The Oscar-winning actress stars with a largely male cast in 'Free Fire', and though she has no problem being the only woman on set, she is left baffled by the way her co-stars like to pass the time.

She said: ''The only thing I've really learned from all the men here is that every surface is a canvas to draw a penis on. Women don't do that. We're not obsessed with drawing boobs everywhere. We're made to feel embarrassed that we have appendages to begin with.

''But men are just like, 'This is my junk'. And each man has a different line he won't cross. Some are like, 'Penis and balls cools - but don't draw hair on the balls, that's taking it too far.' Some won't have stuff coming out of the penis. They're all obsessed with it but they all have a line where they're like, 'No, I won't do that, because I'm a gentleman.'''

And Brie admitted she also didn't share her male co-stars - which also include Sharlto Copley, Sam Riley, Enzo Clienti and Noah Taylor - enthusiasm for their firearms.

She said: ''I feel like the only one who doesn't relate to their weapon. I don't even know what it is. It's smallish.

''The moment I had it out, every guy was, 'Let me take a look at that...' and they were opening it, shooting it, I barely knew how to hold it. I felt so stupid.''

But director Ben Wheatley insists the set wasn't overly macho or ''nasty''.

He told Total Film magazine: ''I work with the same crew all the time and they're not macho so it doesn't get brash and nasty.

''And gender-wise, the crew is quite split. I think that's healthier. I'm not a big fan of locker room talk, even though I've got a filthy, sailor mouth.''