Frozen 2 was the big attraction at Disney Animation's D23 Expo presentation, and attending fans were treated to exclusive footage that included one of the sequel's musical sequences. Directed by Chris Buck and Jennifer Lee, Frozen 2 will continue the story of the enormously successful 2013 movie by delving into the mystery of where Elsa's ice powers came from and the question of what happened to their parents.

The first clip showed a flashback to Elsa and Anna as children, being held by their mother, Queen Iduna (Evan Rachel Wood), who sings them a lullaby. The next clip takes place in the present, with Anna, Elsa, Olaf, Kristoff and Sven are playing charades. However, when it's Elsa's turn she becomes distracted and then brings the game to an end, saying it's time for bed. Kristoff then tries to propose to Anna, but unfortunately she's too distracted by her sister's mood to notice.

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Anna tried to comfort the troubled Elsa by singing her the same lullaby that their mother sang to them when they were children - and the lyrics are pretty significant: "Where the north wind meets the sea/There's a river full of memory/Sleep my darling, safe and sound/For in this river, all is found." While it could be just an innocent song to soothe children to sleep, it's more likely a clue to where Elsa can learn where her powers came from - starting where "the north wind meets the sea." That would certainly fit with the first trailer, which showed Elsa battling to freeze the waves in an ocean storm, and then the group of friends heading out on an intrepid adventure.

The lullaby helps Elsa to fall asleep for a while, but she's awoken by the sound of a voice in her head, calling to her. She at first tries to muffle it with a pillow and, when that doesn't work, she starts to sing. The song is called "Into the Unknown," and it's a big, epic ballad that's likely to be Frozen 2's answer to "Let It Go." As she sings, Elsa wanders through the castle in search of the source of the voice, then eventually chases it out of the castle and follows it off the edge of a cliff by using her powers to create a path of ice.

One theory about Frozen 2's plot is that Elsa is one of four women with special abilities, each corresponding to a different season, and that Elsa's mother had similar abilities - which would explain why her father seemed to know about how to conceal her powers in the first movie. Fans have also theorized that one or both of Elsa and Anna's parents might still be alive (they supposedly died in a shipwreck), and that the movie is about Elsa and Anna journeying to find them.

Based on the positive response from the D23 audience, it looks like Disney has another future classic on its hands with Frozen 2 - and it will certainly be interesting to find out where Elsa's powers come from.

More: Frozen 2 Trailer Breakdown: 16 Story Reveals & Secrets You Missed

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