Natalie Portman Stars in Venice Film Festival Opener

The Venice film festival opens on Wednesday with "Black Swan", a dark psychological drama starring Natalie Portman as a ballerina who finally lands the lead role but loses her grip on reality as the pressure builds.

The arrival of a rival dancer, played by Mila Kunis, triggers both obsessive jealousy and sexual liberation in a plot echoing that of the ballet around which it revolves.

A steamy love scene between the actresses and elements of violence and horror make it a departure from clean-cut on-screen roles often associated with Portman. In a cover story in this past February's issue of Elle U.K., Portman stated that she doesn't like to take on the role of 'sex bombs' in her films.

"(Director) Darren (Aronofsky) talked to me about this (sex) scene in our first meeting eight years ago," Portman told reporters in Venice following a press screening and ahead of the formal evening red carpet world premiere.

"He described it as: 'You're going to have a sex scene with yourself,' and I thought that was very interesting because this movie is in so many ways an exploration of an artist's ego and that narcissistic sort of attraction to yourself and also repulsion with yourself."

Aronofsky won the top prize in Venice -- the Golden Lion for best picture -- two years ago with "The Wrestler", and he said he saw similarities between the two.

"When I started to think about doing Black Swan after The Wrestler, I very much saw them as related to each other," said the 41-year-old.

"The more I looked into the world of ballet, I actually started to see all these similarities to the world of wrestling -- they both have these performers that use their bodies in extremely intense physical ways."

French actor Vincent Cassel, who plays the ballet director, wondered why anyone would want to go into the world of dance. "I think if you want to be a dancer it has to be a vocation. It's like being a priest, really, because you work so hard, you work every day, it hurts like crazy and you make no money. So I guess it's just not something one should do."