Songfacts®:

• This song opens with Wayne Coyne singing about a woman, comparing her eyes to butterflies, her smile to a rainbow and her hair to "sunbeam waves, shining 'round like a halo." He then proceeds to reflect on the song title:
  
  And the castle oscillates to the beating heart of her mind
  And the castle is taller than the Northern Lights
  And the castle can never be rebuilt again
  
  Wayne Coyne wrote the tune after a session one night just singing into his phone. He explained to Uncut: "I liked that idea of singing about the castle as the structure of your life or whatever. I filled the song with lyrics that hint at the fairy-tale world – unicorns and stuff like that – which really hinted towards a new flavor that the Flaming Lips hadn't really explored before."
• Coyne wrote this in the aftermath of a friend's suicide. He wanted to write a song about how he felt but didn't want it to be too bleak. He explained in a Diffuser interview: "You want it to be a story that becomes sad. You can't just open up the first page and say, 'Everybody dies' and it's bleak and the whole story is everybody's dead. That's not a compelling couple of minutes, you know?"
  
  "And then I think I just got really lucky," he continued. "The first line of 'Her eyes were butterflies and her smile was a rainbow,' I thought well in this context, knowing it was going to turn horribly sad, this is helping it feel like, 'Oh, tell me about this person.' Instead of singing about what happened to her, I was thinking I would just make the song about her. And in the music, and in what I'm saying, you would realize what happened to her as the song went."