It was warm and windless during last night’s Opening Ceremonies for the Beijing Olympics, as indicated by the reporters who said so and as evidenced by the spectators who kept fanning themselves and the dust from the fireworks that fell straight down. Can anyone explain the mystery of the vigorously and unidirectionally waving Chinese and Olympic flags? Both started flapping only upon reaching the very top of the flag poles. Hints: there were no giant fans attached to the stadium and a closer shot and the shape of the flags as they were waving said it all. Final hint: this is most effectively explained by a venturesome 18th century Italian physicist, or better yet, by the older Swiss mathematician who happens to be a member of a most talented clan. His principle will really make this idea fly!

Not too sure about this one, but here's a Washington Post article from 2006 issued in the wake of the invention of a "self-waving flag".

http://www.washingtonpost.com/wp-dyn/content/article/2006/06/13/AR2006061301386.html?referrer=email

I was not even aware of that invention, Rami. However that flag looks very different from the way the Olympic and Chinese flags were behaving. If you watched it the other night, you would have seen the aperture built into the flag pole itself, just below the very top. You could see the wrinkling at the middle of each flag and the funnel shape they assumed because of this local pocket of air being blown. See the first link below, just 19 seconds into the photo montage. That is how the flag looked each time it was on camera, not completely unfurled, but tapered towards the free edge.
When a fast car drives by and sucks in dead leaves in its’ wake, when a subway train zooms through a tunnel and drags in newspapers and other debris behind it, these are all demonstrations of the Venturi effect and Bernoulli’s principle.
Basically, when fluids ( or compressed air, which behave like compressed fluids ) are passed through a narrow opening, there is an increase in speed simultaneous with a decrease in pressure adjacent to the area of the narrowing. See the demonstrations below.
A tiny aperture near the top of the flag pole blowing air decreased the relative air pressure in the vicinity of the flags, dragging and sucking them upwards into a semblance of “ waving flags “.
http://www.youtube.com/watch?v=aj02cagXQn0
(19 sec into the video)

http://www.freepatentsonline.com/7017510.html
http://www.youtube.com/watch?v=13eoSasj4hw