What was behind the door?

No, they didn't. I am watching this movie now. We just see her screaming and looking shocked Who knows why?

I think theres nothing behind that door. She claimed that whatever is beind that door made her kill the man. When she finally manage to get the door open, you see Darling screaming. I think thats because she realise theres nothing there and that she's the only one responsible for what she did.

Something to give the meaning and interest to this POS.