Video previewing London 2012 Opening Ceremony released

The London Olympics organizers have done a pretty good job keeping Friday's Opening Ceremony under wraps. Now, at last, they're giving us a glimpse. They've released a 30-second clip from a dress rehearsal that suggests that it will be an extraordinary spectacle, as one would expect from director Danny Boyle (he of Trainspotting and Slumdog Millionaire fame).

The footage shows kids in pj's bouncing on giant beds, and an array of dancers in lavish costumes. The most mystifying — and gripping — image is a mass of helmeted cyclists wearing giant silvery-blue flapping wings, pedaling around in two huge circles.

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