During their Hanukkah residencies, Yo La Tengo cover Jewish songwriters of note in addition to performing songs from their deep catalog. They'd already covered a few Lou Reed / Velvet Underground songs on Night 1, but he's a favorite, so it was not surprising that they would dip into that well again. But you might not have expected Hedwig creator John Cameron Mitchell to come out to sing with them midway through the band's Night 4 set. where they were already augmented by CUP, the duo of Nels Cline and Yuka Honda. JCM sang Velvet Underground song "I Found a Reason" and then Lou solo song "Waves of Fear." Video of both of those covers is below.
Usually guests come out for covers during the encores at the Hanukkah shows, but John said he had a flight to Utah to catch so he could "kiss some Mormon boys." JCM also joined joined YLT in 2018 and you may remember that Yo La Tengo collaborated with Yoko Ono on a song for 2003 Hewig tribute album, Wig in a Box.