<P> En route to a weekend getaway, surgeons Arizona Robbins (Jessica Capshaw) and Callie Torres (Sara Ramirez) are involved in a vehicular collision, moments after Robbins proposes marriage . Torres suffers severe injuries, which endanger both her life and the life of her unborn child . She and Robbins are taken to Seattle Grace Mercy West Hospital, the institute at which they both work . Their colleagues attempt to save Torres, while Robbins and Mark Sloan (Eric Dane), the father of Torres's baby, stand by . Torres's many injuries include neurological trauma . While barely conscious, she hallucinates an uninjured version of herself standing beside her . The hallucinatory Torres begins to sing, and is gradually joined by the doctors treating her . This singing continues throughout the episode, as Torres's projection of herself attempts to reach out to Robbins . </P> <P> Torres goes into cardiac arrest and is taken into an operating room she is temporarily stabilized, pending further surgery . She is moved into intensive care, while neonatal surgeon Addison Montgomery (Kate Walsh) is flown in by helicopter in case the baby has to be delivered prematurely . Robbins and Sloan argue over Torres's treatment; Robbins believes that Torres would not risk endangering the baby, but Sloan argues for saving Torres at all costs . The attending surgeons devise a treatment plan, led by trauma surgeon Owen Hunt (Kevin McKidd). As they do so, Torres dreams about the moments preceding the accident . Her dream self sings to Robbins, interspersed with shots of the hospital staff singing and dancing with their own partners . Dr. Cristina Yang (Sandra Oh) suggests treating Torres with a high - risk but potentially effective cardiothoracic procedure she learned from her old mentor, Preston Burke (Isaiah Washington). Her current mentor, Teddy Altman (Kim Raver), refuses to perform it, but when Torres's condition deteriorates and she is rushed back into surgery, Hunt agrees that Yang should attempt the procedure . </P> <P> When Torres again goes into cardiac arrest, Montgomery delivers her daughter at twenty - three weeks's gestation . The baby is initially unable to breathe, so with Sloan's support, Robbins steps in and is able to revive her . Across the operating room, Torres's condition begins to improve . Once the surgery is complete, the doctors deal with their own affairs; Sloan's former partner Lexie Grey (Chyler Leigh) commits to her new relationship with resident Jackson Avery (Jesse Williams); Lexie's sister (and series main character) Meredith Grey (Ellen Pompeo, primary series star) confesses that she was jealous of Torres's pregnancy, which prompts her husband Derek Shepherd (Patrick Dempsey) to promise that they will have a child together; Altman tells Yang that she can no longer teach her; Sloan and Robbins bond over their shared parenthood . Later, as Robbins keeps a vigil by Torres's bedside, the hallucinatory Torres is able to rouse her recovering self . As she regains consciousness, Torres accepts Robbins's proposal . </P> <P> Since Grey's Anatomy began, series creator Shonda Rhimes had planned to produce a musical episode . She first discussed the idea during filming of the pilot episode, when the program was as yet untitled . Rhimes felt that seasons six and seven were the right time for the crew to "try anything and everything (they had) always wanted to do," and explained that she "finally (had) the right idea and the right talent to make (a musical episode) happen ." Filming began seven and a half years after Rhimes initially raised the idea . The episode was shot in approximately two weeks . Though cast member Dempsey jokingly referred to the episode as Glee M.D., Rhimes intended for it to differ from other musical television episodes . She called it the opposite of "Once More, with Feeling," the "all - out, show - stopping," musical episode of Buffy the Vampire Slayer, as she aimed to "do something that was musical without being a musical ." </P>

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