This modern era of moviemaking has plenty of peculiar challenges for actors -- on green-screen sets, for instance, they have to watch a ping-pong ball hanging from a string and convince the camera that they actually staring down some magical beastie -- but for the actors auditioning for "Avatar" the biggest challenge may have been reading a sheet of paper with words invented by a USC professor named Paul R. Frommer.

Frommer, a linguistics specialist, was brought in by "Avatar" writer-director James Cameron to create an entire functioning language for the tribe of 10-foot-tall blue aliens who inhabit Pandora, the setting for the film's conflict. Frommer tackled the project with glee -- "How often do you get an opportunity like this?" -- but the actors who had bend their tongues around the invented vocabulary and syntax were slightly less charmed by the experience.

(...)Frommer didn't start completely from scratch; Cameron had come up with about three dozen words of the Na'vi language at that point in his project document, which was like a quasi-script or a long treatment ("They called it a scriptment," Frommer said, "and that was a new word to me")  but most of the words  were character names.

(...)Frommer prepared three "sound palettes," which were collections of words and phrases that did not have meaning but did have the cadence and feel of languages. Cameron mulled over the sound files and picked the third as the best fit for the world he wanted to hear. He did not want tonal differences and variations in vowel length, for instance, but he loved the ejectives.

Then came the heavy lifting -- nailing down the sound system, word construction, the rule of syntax -- and Frommer immersed himself in the thousands of decisions required, many of them deciding what goes in and what goes out. The Na'vi language, for instance, does not have the sounds buh, duh, guh, chu, shu, and by restricting the sounds, Frommer said, a characteristic shape of the language begins to distinguish itself.