Unique Daily has the time lapse video clip: Link

I saw that "chalk shadow art" is making the round on the Net, without attribution or explanation (sigh). So, with a little Googling, I found the back story to the phenomenon:

Earlier this year, Mr. Gallagher was mugged on his way home from a shift at Bar Tabac on Smith Street, where he worked as a waiter. "I turn around and this guy’s got a two-foot machete in my face," he said.

Mr. Gallagher was unhurt and the mugger was later caught by the police, but one night soon after the mugging, with the image of his attacker’s dark silhouette still burned into his memory, Mr. Gallagher was mesmerized by a shadow on the sidewalk. He reached into his pocket and felt the chalk he had used to write the outdoor menu at Bar Tabac, and he dropped to his knees to outline it.

Shadow art was born.

Now Mr. Gallagher heads out on foot or on his bike with a backpack full of chalk, looking for shadows to trace. When he tells you that "everything is fair game," he means it. He has traced everything from hydrants to whole city blocks.

Conrad Mulcahy of The New York Times has the story: Link