One "Seven" got sold, it went through a number of rewrites that softened the story. One of the biggest sticking points of course was the climactic "head in the box" scene, and it was originally eliminated (via Uproxx) after Walker turned in his first draft.
But Fincher was sent the first draft by mistake, and as he read it, he was morbidly intrigued. At first he thought it was just going to be a buddy cop movie, but it turned into something much deeper and disturbing. "All of a sudden it took this turn," he told Empire (via Cinephilia Beyond). "And I found myself getting more and more trapped in this kind of evil, and although I felt uncomfortable being there, I had to keep going."
Finally Fincher asked, "Are they going to make this? There's this head in the box at the end, it's just amazing." When they sent him the watered-down draft, Fincher responded in no uncertain terms that he wanted to film the original ending.
As De Luca recalled (via Deadline), "There was a draft that had a softer ending without the head in the box, but everyone, from David to [New Line founder] Bob Shaye on down, felt the ending made it a provocative water cooler movie."
