Lady Gaga goes crowd-surfing at Lollapalooza

Lady Gaga was a headliner at Lollapalooza over the weekend, and tens of thousands of people jammed Chicago's Grant Park to see her perform. But they might not have gotten the best Gaga show of the festival.

A few hours before she took the main stage on Friday (Aug. 6), Gaga made a surprise appearance on a side stage during the band Semi Precious Weapons' set. Or, rather, on a stage and in the crowd.