From left, Melissa Cohen, 32, and Tom Harrigan, 29, juggled while Justine Underhill, 23, rode her unicycle, and Theerasak Punngam, 25, jumped onto a slackline at Meridian Hill on June 24. Slackliners, who meet here from 3 to 7 p.m. on Sundays, are a relatively new addition to the decades-old drum circle crowd at the park.