Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
This is about an actress named Elizabeth (Natalie Portman) who spends time with a woman named Gracie (Julianne Moore) because she is going to portray her in a movie. Gracie was an elementary school teacher who went to prison 20 years earlier for raping a 13-year-old boy named Joe (Charles Melton) after which they got married and raised their children. It's based on the story of Mary Kay Letourneau, a 34-year old teacher who went to prison for having a sexual relationship with her 12-year-old student in the mid 1990s, then had his children and married him. There is a long scene at the end with a live snake.
At the very end of the movie, after Elizabeth has crossed some ethical lines in her relationships with Gracie and Joe, possibly ruining their lives, we see some unfinished documentary footage that shows Elizabeth and a boy actor performing a scene in the movie about Gracie that she is making. The footage shows a large film crew and Elizabeth and the unnamed actor portraying the 13-year-old Joe (Rocky Davis) set in a location that is supposed to be the pet store where Elizabeth worked and met Joe. Elizabeth holds one of the pet store snakes, stroking it seductively, telling Joe it won't hurt him and convincing him not to be afraid of it. She is essentially seducing young Joe, using the snake to convince him not to be afraid of her advances. The snake was not dangerous, but ultimately Gracie was, taking away his innocence. It's the very last scene in the movie, and the director really wanted us to see this interaction, which is repeated three separate times. I'm not sure exactly what the director is trying to say, but it's more about Elizabeth than it is about Gracie. It's an art movie, so there will be more than one interpretation. The scene is intentionally disturbing because we're watching an act at child molesting, and the use of the snake is going to make it even more upsetting to much of the audience since so many people dislike snakes.
The dialog for the scene is this:
Gracie (Elizabeth): "Are you scared?"
Joe (Rocky): "No."
Gracie (Elizabeth): "It's okay to be scared."
Joe (Rocky): "I'm not."
Gracie (Elizabeth): "She doesn't bite."
Joe (Rocky): "How do you know?"
Gracie (Elizabeth):"She's not that kind of a snake."
The second time they do the scene Elizabeth talks more softly.
The third time they do the scene Elizabeth is even more sultry and seductive, whispering her lines.
After the third time the director says he has what he needs, but Elizabeth convinces him to let her do the scene again because it is getting more real for her, as if she thinks she is really seducing the boy actor.
The director reluctantly calls action for the fourth time and we see a close-up of Elizabeth, then the film ends.
The snake we see is an albino corn snake, a common pet store snake now and back in the 1990s when the scene is set. We even see the snake's terrarium on the floor of the set for added realism.