Justin Timberlake has been on a tear through 30 Rock lately, appearing on Late Night with Jimmy Fallon three nights in a row to promote his forthcoming album, "The 20/20 Experience." Call it a residency, if you will. Last night he sat in as the fifth member in Jimmy Fallon's barbershop quartet, The Ragtime Gals, to perform an acapella version of "SexyBack." Hope Fallon's staff has an OBGYN on speed dial, because all the women in the audience got pregnant:

Oh yeah, his performance of "Mirrors" later on in the show was awesome. It's a good JT jam: