Paul McCartney at Bonnaroo 2013

Paul McCartney performs at Bonnaroo 2013.

Charli XCX's boy band analysis, Solange's Fugees cover, late-night show surfing, and more from Bonnaroo Day 2.

Friday (June 14) at the 2013 Bonnaroo festival began and ended with headliner chatter: in the morning, it was confirmed that Jack Johnson would be taking over for Mumford & Sons on Saturday night, and in the evening, Paul McCartney played three hours' worth of timeless hits, and threw in some fireworks for good measure (read a full recap of Macca's headlining performance here). In between was a slew of deeply enjoyable sets from artists kicking it in Manchester, Tenn., from Passion Pit's exuberant showcase to Of Monsters and Men's tightly packed performance to a double-dip of Solange before her proper set took place on Saturday.

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Check out 10 things seen and heard on the second day of the annual hippie haven: 

1. Jack Johnson got a call around 7 p.m. Thursday night when he was offered the Saturday headlining slot at Bonnaroo, taking the place of the just-canceled Mumford & Sons. He was already his way to the festival for a surprise performance with Brushfire labelmates ALO later that night, and accepted the festival's offer as he scrambled to put together a setlist. Considering his last Bonnaroo set included a guest appearance from Eddie Vedder, might Johnson have some other surprises in store? Just a confirmed duet with ALO for now, he told Billboard in the media tent, and more stripped-down arrangements to accommodate the largely acoustic vibe of his new album "From Here To Now To You."

Bonnaroo 2013 Video

2. During her early afternoon set, U.K. pop starlet Charli XCX once again unfurled her emotional cover of Backstreet Boys' "I Want It That Way," which pairs the boy band classic with aching undertones. In the media area after the performance, the 20-year-old said that she preferred BSB to rivals *N SYNC -- although she does enjoy the latter's hit single "Pop." When asked if she enjoys any of the current crop of boy bands, Charli flatly replied, "No."

3. Positioned as a star-studded cultural celebration following Paul McCartney's Friday headlining set, the first Bonnaroo Hip-Hop Superjam lived up to its billing, with artists like DJ Jazzy Jeff, the Neptunes' Chad Hugo and surprise guest the RZA among those tossing out classic rap cuts. The two highlights: ScHoolboy Q's first-ever live performance of "Collard Greens," a Kendrick Lamar-assisted track from his upcoming debut album "Oxymoron"; and Solange sashaying onstage in dreadlocks and tackling a cover of the Fugees' "Killing Me Softly." One year after D'Angelo returned for his first U.S. performance in over a decade at a Bonnaroo Superjam, this year's stellar mish-mash of hip-hop artists made the case that this should be a yearly occurrence within the genre.

4. Passion Pit's Michael Angelakos was among the guests on a 1:00 panel discussing the different ways bands approach the festival circuit in the press tent. The panel also included Ed Helms, John Oates and Matt & Kim. Angelakos candidly admitted that the first time Passion Pit played Bonnaroo in 2009, he was so underdeveloped as a performer at the time he can barely remember playing the gig now. He's much prouder of the band's musicianship today, however, and credits spending the better part of the last year on the round for his confidence boost. There's also the matter of his impossibly high falsetto, which is used in full force on virtually every song in Passion Pit's catalog. Angelakos told Billboard after the panel that he maintains his vocal gymnastics on the road using a combination of water, sleep and minimal drinking. "I've also been doing it enough that my voice has developed new muscles, so it's easier now for me to that register," he said.

5. The xx began their set on the Which Set minutes before midnight, and when the clock struck 12:00, it was officially frontman Oliver Sim's 24th birthday. When asked beforehand if the indie-pop group was going to acknowledge his birthday at all during the set, Sim laughed and replied, "No no, I'll probably just have some champagne or something backstage." Nevertheless, a pocket of fans in the group's crowd began belting the "Happy Birthday" song, seemingly for Sim, during the xx's haunting performance of "Heart Skips a Beat."

6. Of Monsters and Men drew one of the biggest crowds to the Which Stage (Bonnaroo's second-biggest platform) on Friday afternoon, staying jovial while playing cuts from their "My Head is an Animal" album as well as a cover of Yeah Yeah Yeahs' "Skeletons." Strangely, the group performed their breakout hit "Little Talks" with two songs still to go; the timing thinned out the crowd while the folk group wrapped up with ornate renditions of "Six Weeks" and "Yellow Light."

7. The third season of "Game of Thrones" may have just wrapped, but Bonnaroo attendees still have the ongoings of Westeros on the brain. One large instance of sanctioned graffiti on a festival barrier read in block letters, "KILL KING JOFFREY."

8. Aside from her part in the evening's Hip-Hop Superjam, Solange was on hand for a surprise guest spot earlier in the day: during Grizzly Bear's early evening set, Ms. Knowles hopped onstage to perform backing vocals on "Two Weeks." Though her presence was subtle, it helped take the choral majesty of its chorus to new heights.

9. Passion Pit brought their crowd-pleasing indie pop to the main stage for a late afternoon set. Frontman Michael Angelakos pointed out the band had played twice before -- in 2009 and 2010 -- and expressed gratitude to be on its biggest stage. They played a great deal from last year's sophomore effort "Gossamer," including a show-stopping performance of "Take a Walk," with the audience belting the titular lyrics along to the chorus. Still, their helium-voiced breakout song "Sleepyhead" was the climactic moment as the set closer.

10. By the early morning hours, Paul McCartney's authoritative headlining set was over and other big names like ZZ Top and the Hip-Hop Superjam were calling it a night. But after 1:00 AM, the 'Roo fairgrounds stayed bustling, with many fans still out and about, searching for what the wee hours had to offer. Sets from EDM titans Pretty Lights and indie experimentalists Animal Collective raged long past 3:00 AM, giving the night owls something to move their feet to. Even those at the Animal Collective's set could see the sky illuminated by the appropriately awe-inspiring neon light spectacular from their counterparts.