They only forgot to sing during the opening! Dressed in white wedding attire, IU and Nicole performed Madonna’s Like a Virgin at the 2010 SBS Entertainment Awards. It was only a small slip; it wasn’t very noticeable since the song was pre-recorded. They were so focused on getting the choreography right that they both forgot to sing the beginning lyrics! It’s okay, just a small mistake. Singing and dancing are very hard - at least that’s what I think. I’m still amazed that idols can sing and dance so well at the same time, no joke.

Source