Fifty Shades of Grey is sure to be an R-rated box office juggernaut upon its February 13 release. But as the old adage goes, sometimes it’s best not to see how the sausage is made.

Case in point: director Sam Taylor-Johnson has revealed there was a fair amount of off-screen tension between her and E.L. James, the author of the Fifty Shades trilogy.

Speaking with Porter magazine, Sam admits the two of them often couldn’t see eye-to-eye on the film’s direction.

“It was difficult, I’m not going to lie,” she notes. “We definitely fought, but they were creative fights, and we would resolve them. We would have proper on-set ‘barneys.”; (British slang for intense arguments).

She added, “I’m not confrontational, but it was about finding a way between the two of us, satisfying her vision of what she’d written as well as my need to visualize this person on-screen, but, you know, we got there.”

Fortunately, both women seem very happy with the end result. And despite managing to avoid an NC-17 rating in the U.S., Sam says the film is “going to be extreme… pretty sexually explicit.”