She masturbated with a wine bottle!

It wasn't masturbation Einstein.

Go Back To The Grave.

It was sodomy?

Correct

Get on the scale! Get off the scale.

It was neither masturbation, nor sodomy. She inserted the top of the wine bottle in her vagina and aggressively pushed it back and forth to make sure her vagina suffered "real trauma" in case the doctors inspected her after claiming she got raped, which they did.

That was also what she was doing with the twine she wrapped around her wrists earlier in that scene; she wanted to make sure there was "physical evidence" that she was raped (which we all know she wasn't).

Erm it's a movie. She didn't do anything of the sort, Rather her character Amy Dunne did it fictionally.

Get the difference?

In Gone Girl, Amy Dunne wants to tell the police that she has been raped, so to do that she needs physical evidence for a rape exam. So to cause some trauma around her vulva and vagina area, she shoves a wine bottle up it. I will admit that it was left fairly vague in the film, but it is very apparent in the book, and hey - this is one of those movies where you should've read the book anyway.