McG, the director of the upcoming "Terminator Salvation," revealed that the fourth film in the Terminator franchise might feature a visual effect "that's never been done before."

The director confirmed in his official blog that the project had wrapped principal filming and is now in post-production. Charlie Gibson and his special effects crew are trying to push the boundaries of their craft with one scene in particular.

"At some point the effects kick in and like any Terminator fan, Charlie wants his mind blown," McG said. "There's one sequence in particular where we're trying to achieve something that's never been done before. I don't want to talk about it because we haven't been successful yet ... But we're working on it."

McG revealed no more about this scene, but he did write about the film's stars, Christian Bale and Sam Worthington, and about the global scope of his film.

"Christian and Sam bring power to the rolls of John Connor and Marcus Wright," McG said. "This is a story of two destinies colliding. Connor is part of a resistance comprised of the ethnicities that make up the globe. This film is so much more that just Los Angeles. It reflects the global crisis of man, all of man versus machine."

"Terminator Salvation" also stars Anton Yelchin, Bryce Dallas Howard, Moon Bloodgood and Common.

The film is slated for a May 2009 release.

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