For a band whose sound is so manic, Yeasayer played it cool during their Friday afternoon set. The Brooklyn quartet's African beats, tropical samples and Middle Eastern drones brought a taste of the world to Grant Park, while its loose grooves kept the mood laid back and the audience cool. Percussion reigned supreme. Nothing that could be hit with a mallet, drumstick or hand was safe. And despite the serious look on his face, vocalist-keyboardist Chris Keating spread positive messages and entertained with robotic dance moves. Songs such as "Wait for the Summer" and "2080" rattled with psychedelic intent, while "No Need to Worry" summed up why the group's music went down so easily.