Ask any Grey's Anatomy fan which episode was the most shocking and they'll say the musical episode. Season 7, Episode 18 — titled "Song Beneath the Song" — didn't surprise viewers because of a devastating patient death or a long-awaited hookup between doctors. We all simultaneously scratched our heads when the doctors we'd grown to know and love broke out in… song.

"I have been wanting to do it since we made the pilot basically," creator Shonda Rhimes said about the infamous episode at the time. "We needed it to make sense for our show. Plus, I had to convince the network, which took me seven years." At least they had Sara Ramirez (who played Callie Torres) on the show who also happens to be a Tony-winning singer.

That's why it wasn't surprising that the entire storyline of the episode followed a comatose Callie as the doctors raced to save her (and her baby's) life after she was in a car accident with Arizona Robbins (played by Jessica Capshaw). "That story was destined to happen whether or not there was singing in the episode," Shonda continued. "It just turned out to be the exact right way for singing to happen."

But, Sara wasn't the only cast member to sing. In fact, the entire cast underwent vocal training from Rachael Lawrence — who worked with members of the Glee cast — and spent hours in the recording studio. "I'll never have this chance to be able to do something like this on this show again," Chyler Leigh, who played Lexie Grey and sang "Breathe (2AM)," said. "It was an opportunity for me to really be able to explore that side of me that I've always wanted to but just have been too afraid."

Honestly, we're still not over the fact that our favorite doctors belted out some of the most beloved Grey's music. Songs like "Chasing Cars" and "How To Save a Life," which were played during past monumental scenes were reprieved in an original way for the musical episode.

“There were many times where I felt like, ‘Oh my gosh, we're doing the best episode of Grey's Anatomy ever," Jessica admitted. "And there were other times where I thought, ‘Did we drink the Kool-Aid and we're all terrible?’"

Join our Facebook group for the latest news and updates on Grey's Anatomy!