I dredged this up from the wwftd archives:

the worthless word for the day is: walla-walla

an unintelligible sound made by many people talking at once [from a Hindi word]

In the theater, a walla-walla scene is one where extras pretend to be talking in the background -- when they say "walla-walla" it looks like they are actually talking.

...perhaps shanks can confirm this one.