Who is the third girl in “Black Swan”?

Question

In the 2010 movie Black Swan, Nina and Lily are the two main characters, but a couple of times in the movie, a third girl pops up out of nowhere. I cannot find any information about who this third girl is or even anyone asking who she is (or even who played her).

She pops first when Nina is “exploring herself” in the bathtub (figure 1), and again during the sex scene (figure 2). I thought that maybe she has something to do with sex, but she did not show up in the scene when Nina woke up and… failed to notice her mother sitting next to the bed.

The closest I can come to finding an explanation is a theory about Nina possibly spawning a new personality, which might make sense since the girl looks a little like her, but it seems that people that propose that theory are actually talking about Lily being the new personality, not this third girl. One person seemed to be wondering the same thing, but the answer they got again referred to Lily, not the mysterious, unnamed girl.

I had wondered if maybe she is a morph between Nina and Lily, but doesn’t really seem to be. Whether she was CG or an actual actress, the filmmakers specifically and purposely made a point of putting her in and even highlighting her appearances, so she must be relevant.

Does anyone have any ideas why they put this other girl in the movie and who/what she is supposed to represent?

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Figure 1: The mysterious girl shows up during the bathtub scene and looks similar to Nina

Figure 2: The mysterious girl shows up again during the sex-scene and looks different

Answer 1

The 'Girl' you are referring to is, as you have speculated, a computer generated re-rendering of the principal actress' face.

Fox Studios released a visual effects Show reel 2 years ago, demonstrating the different processes employed to create the special effects and the visual palate of the film.

The video demonstrates the repeated use of 'Head Replacement', whereby Natalie Portman's face is rendered over the top of other on screen characters; notably the rest of the Swan Lake ballet cast.

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The sex scene you refer to is ostensibly an entire fabrication. Nina is suffering from some kind of undiagnosed psychotic episode, the details of which are being discussed elsewhere on the site.

However, Psychiatrists have claimed the character suffers from a Psychosis, but not necessarily Schizophrenia.

But speaking as a psychiatrist, Lamberti said the film did not accurately depict schizophrenia, as has been widely speculated, but "does present a reasonable portrait of psychosis."

"People tend to be scared of things they don't understand," he said. "If you have never treated or observed a person with psychosis, it's upsetting."

Psychosis is a loss of contact with reality that usually includes false beliefs or delusions, and seeing or hearing things that are not there.

Like a fever, psychosis is a symptom rather than a disease, and can be caused by a variety of triggers: exposure to mercury (the hats of the Mad Hatter were impregnated with the heavy metal), drugs like amphetamines, epilepsy, a brain tumor, dementia or psychiatric disorders like schizophrenia.

The technical implications of this, however, suggest that Natalie Portman's face was rendered over Mila Kunis'.

Answer 2

this video at least explains the picture above!