Bonnaroo's always big on surprise collaborations, and last night yielded a pretty huge one. During Earth, Wind & Fire's set last night, the band looked over at the side of the stage and saw Chance the Rapper and Kendrick Lamar watching. They invited the two MCs up to freestyle. Watch video below via Fake Shore Drive. Update: Their full set has surfaced. Watch Kendrick and Chance walk out around the 1:15:00 mark.