Freestyle can be performed a capella, over beatboxing or over instrumental versions of songs. The rhythms and metre are more relaxed than in general rap, so that there is room for improvisation.

Gavin Tyte -- or TyTe, as he's known when he's in hip-hop mode -- has garnered more than 15,000 YouTube views with 'The Beatbox Nativity,' his rap retelling of the Christmas story ...

That leads to the guys recreating the song, with Sean beatboxing and Jimmy rapping. So, when I spoke with Luke Tennie, I asked what it was like to film the silly little gag with Jason Segel ...