Frozen Fever is a 2015 American computer-animated musical fantasy short film produced by Walt Disney Animation Studios and released by Walt Disney Pictures. A follow-up to the 2013 feature film Frozen, the short follows Elsa as she attempts to throw a surprise party for her sister Anna with the help of Kristoff, Sven, and Olaf. Chris Buck and Jennifer Lee again served as the directors with Kristen Bell, Idina Menzel, Jonathan Groff, and Josh Gad reprising their roles from the first film. Production on Frozen Fever began in June 2014 and took six months to complete. The film debuted in theaters alongside Walt Disney Pictures' live-action remake of Cinderella on March 13, 2015. It received positive reviews from critics, along with praise for its original song "Making Today a Perfect Day" by Kristen Anderson-Lopez and Robert Lopez. One year after the events of Frozen, Queen Elsa is determined to give her younger sister, Anna, a perfect surprise birthday party and enlists the help of Anna's boyfriend Kristoff, his reindeer Sven and the lovable snowman Olaf in order to make sure the party goes ahead without any problems. Anna is led on a party treasure hunt created by Elsa, following a piece of string that leads to different gifts. The day starts fine but Elsa suddenly starts developing symptoms of a cold. With each sneeze, Elsa unknowingly produces a group of "Snowgies", little snow-babies who begin to dismantle the birthday party's decorations while Kristoff & Sven try to stop them and Olaf embraces them. Elsa brushes away Anna's growing concern regarding her constant sneezing, assuring her she "doesn't get colds" and enthusiastically continuing the treasure hunt. Meanwhile, Anna is visibly struggling under the weight of all the extravagant presents she has found from the hunt and Elsa's condition is rapidly worsening. Anna recognises her sister is delirious with a fever as they climb the clock tower to Elsa's final present, two figures of the sisters as part of the hourly clocktower procession.