The most infectious earworm of the moment is actually a jam from last August. Train's summery song, 'Hey, Soul Sister,' has risen to No. 1 on the iTunes chart, just in time for warm weather and sunny days. The hit has also sold more than 2 million copies, designating it double-platinum, according to a new press release.

"When people hear it, I think that what I hear mostly is that they're instantly happy," singer Pat Monahan told PopEater. "And I know I felt like that when I heard it first. After it was written, you go like, 'Wow! I'm so happy all of a sudden.'"

Back in November, Monahan and guitarist Jimmy Stafford dropped by PopEater to perform the delicious track unplugged, just a voice, a ukulele and a little rhythm shaker thingy. Did we mention we love us some ukulele? Check out the clip below: