One “seven” was sold, it went through a series of rewrites that softened the story. One of the biggest sticking points, of course, was the head-in-the-box climactic scene, and it was originally left out (via Uprox*) after Walker turned in his first draft.
But Fincher had been sent the first draft by mistake, and as he read it, he was morbidly intrigued. At first he thought it would just be a movie about buddy cops, but it turned into something much deeper and more disturbing. “Suddenly things took such a turn,” he told Empire (via Cinephilia Beyond). “And I found myself more and more trapped in this kind of evil, and even though I was uncomfortable being there, I needed to keep going.”
Finally Fincher asked, “Are they going to do it? At the end there is this head in a box, it’s just amazing.” When a diluted draft was sent to him, Fincher replied in no uncertain terms that he wanted to film the original ending.
As De Luca recalled (by deadline)“There was a softer draft with no head in the drawer, but everything from David to [New Line founder] Bob Shaye, feeling that the ending turned the film into a provocative film, cooler than water.”