This is the almost-title track to Florence + The Machine’s debut album. Lungs was later re-released with a special Between Two Lungs edition, solidifying this.

Welch told the story of the song on her website:

That was the first song I ever wrote by myself, so it’s crazy to me that it’s on the album. I was still at art college, but my first guitarist, Matt [Allchin, of The Ludes], had left and I wasn’t sure how I was going to be making music. I was still doing gigs, but I wasn’t sure what was going to happen. It started with the drums, dum, dum. I’ve always been interested in the lulls between notes and the atmosphere that silence creates. It’s all about the build, and the final release – the euphoria that you can get from music. But the silence around it, and the studio hiss – I love studio hiss!
It’s a song being built by someone who has no idea how to play anything, and is making it all up as they go along. The title actually comes from an 80s pulp book I’d found in a second-hand shop. It has some great titles in it. It became about a kiss – the air you share when you’re kissing someone. And the way it fills you up, and you don’t want the bubble to burst.

Speaking to Steve Lamacq, Florence mentions:

That song uses the first piano melody I wrote was for Between Two Lungs, which is literally just an ascending scale.