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Sia Becomes A 'Bird Set Free' With This Adele Leftover Song

But the song is still clearly all about Adele.

If you don't know the backstory of Sia's latest single, "Bird Set Free," you might think it's an exciting anthem about her stepping out from under the thumb of some wing-clipping, voice-silencing tormenter. But when you find out the song was originally co-written with and cut by Adele for 25, well, that changes the story entirely.

Like "Alive," Sia's first track released from her new album This Is Acting, "Bird Set Free" was co-written by the two mononymous singers -- one of three total that they came up with -- with the intention of having Adele include it on her 25 album. And even though Adele did record the song for her album, it didn't make it onto the final track list.

"She actually did cut that one, but then at the last minute, she was like 'everybody is saying that it just sounds like a Sia song,'" Sia explained to Ryan Seacrest in September.

And while, yes, the pace and arc of the song are so very Sia, the lyrics are a complete reminder of the struggle Adele endured a few years ago with her vocal cords.

"Clipped wings, I was a broken thing/Had a voice, had a voice but I could not sing": In 2011, Adele suffered a vocal cord hemorrhage from a benign polyp and was forced to cancel several shows to undergo laser microsurgery to repair the damage.

"Had a voice, had a voice but I could not talk": After her surgery, Adele was ordered not to speak for two months.

"I'm not gon' care if I sing off key/I find myself in my melodies/I sing for love, I sing for me/I shout it out like a bird set free": Adele's surgery was a complete success, but even if things hadn't returned to normal, it sounds like she wouldn't have given up on her love of music.

"Now I fly, hit the high notes/I have a voice, have a voice, hear me roar tonight/You held me down/But I fought back loud": In 2012, Adele returned to the stage at the Grammys with a triumphant comeback performance of "Rolling in the Deep."