Rihanna and Eminem are set to go out on a co-headlining tour in less than a week, and the duo offered a little taste of what's to come during the latter's Friday night set at Lollapalooza. Deep into Em's show, he brought out his frequent collaborator for renditions of their Marshall Mathers LP 2 team-up "The Monster" and their haunting 2010 duet "Love the Way You Lie." More surprisingly, Rihanna also sang on a version of "Stan." You can catch that above, and the other two tracks below via Stereogum. Expect more surprises once the "Monster" tour kicks off August 7 at Pasadena, California's Rose Bowl.