"As hard as it was at times - because these things are very hard to make, they are a storm happening all around you every day for six months - we made a pact to try to make each other laugh as much as possible."
In a fab montage, the pair go on a recruiting drive, in which they perch on a strip-club bed.
"That scene got exceptionally silly at one point," says McAvoy. "I don't know if I'm even allowed to tell you what originally happened. But it got pretty f---in' kinky. I'm not joking."
Was the dashing duo's bromance, uh, consummated?