The idea of 'The Sing-Off' (Mon., 8PM ET on NBC) is that we get to hear songs like we've never heard before. This week, for doo-wop group North Shore, it was a chance for them to sing a song they'd literally never heard before.

The old school a cappella group admitted that none of them even listen to the radio anymore, so they didn't know who Bruno Mars was before they got assigned his hit 'The Lazy Song.' Nevertheless, they presented a version of the song that was true to the original, and yet sounded completely theirs.

There were a lot of great performances in this fourth week of 'The Sing-Off' featuring six of the remaining twelve acts. We can't wait for these brackets to unite into a single group of finalists so we can see everybody every week, though!

How much of Swingtown is real and how much is pure fiction? According to Mike Kelley, Swingtown's creator, there are elements in the show that come right from his childhood memories of growing up on the North Shore, a trendy suburb of Chicago. But the sex and the swinging? That's mostly creative license.

So were there really sex parties and swinging in the Kelley home? "You know, it comes from imagination, for the most part."

Inspired by 1976, the era of women's liberation, disco-dancing, the end of the Vietnam War, and sexual freedom thanks to the pill and no AIDS, Kelley balances the fantastic elements with nostalgia.