Recording artist Ariana Grande performs onstage during the 2014 iHeartRadio Music Festival at the MGM Grand Garden Arena on September 19, 2014 in Las Vegas, Nevada. (Photo by Kevin Winter/Getty Images for iHeartMedia)

Trevor Olson, from Minnesota, dressed as the character “Joker”, poses for a photograph at New York's Comic Con convention, October 9, 2014, in New York City. The event draws thousands of costumed fans, panels of pop culture luminaries and features a sprawling floor of vendors in a space equivalent to more than three football fields in Javits Center. (Photo by Shannon Stapleton/Reuters)

“A Mothers Tail”. A baby cub pulls on his mother's tail to get attention. Photo location: Masai Mara, Kenya. (Photo and caption by Tori Marsh/National Geographic Photo Contest)

Miss California Crystal Lee performs during the Miss America 2014 pageant, Sunday, September 15, 2013, in Atlantic City, N.J. (Photo by Mel Evans/AP Photo)

Taylor Swift performs “All Too Well” at the 56th annual Grammy Awards at Staples Center. (Photo by Matt Sayles/Invision)

Runners cross the Verrazano-Narrows Bridge shortly after the start of the New York City Marathon in New York, November 2, 2014. (Photo by Lucas Jackson/Reuters)

Iggy Azalea (L) and Ariana Grande perform onstage during the 2014 Billboard Music Awards held at MGM Grand Garden Arena on May 18, 2014 in Las Vegas, Nevada. (Photo by Michael Tran/FilmMagic)

A festival goer uses a hula hoop, as revelers gather ahead of this weekends Glastonbury Festival of Music and Performing Arts on Worthy Farm in Somerset, southwest England, on June 25, 2014. US metal giants Metallica will play this year's coveted Saturday night headline spot at Britain's Glastonbury festival, organisers announced Thursday. It will be the “Master of Puppets” four-piece's first appearance at the legendary festival, held in south west England, following on from The Rolling Stones' Worthy Farm debut last year. (Photo by Leon Neal/AFP Photo)