Three years in the making, Biophilia involved input from a variety of sources including National Geographic and Apple. Bjork wrote this song after taking part in a DNA survey on National Geographic. She told NME: "On both sides, I was from boat people."
Bjork explained the song's meaning: "It's just the feeling when you start thinking about your ancestors and DNA that the grounds open below you and you can feel your mother and her mother, hand her mother, and her mother, and her mother 30,000 years back. So suddenly you're this kinda tunnel, or trunk of DNA… All these ghosts come up so it ended up begin a Halloween song and quite gothic in a way… It's like being part of this everlasting necklace when you're just a bead on a chain and you sort of want to belong and be a part of it and it's just like a miracle."
Biophilia, in collaboration with Apple, features unique apps for all ten tracks created to add multiple dimensions to each song. Bjork explained this song's app to NME: "You can see how DNA moves. Each protein is a part of the song. And you can cue up what you want to happen."
Björk collaborated with biomedical animator Drew Berry for the music video, which explores the inside of the singer's body. Berry explained: "The 'Hollow' music video is a powers-of-10 exploration of the microscopic and molecular landscapes inside Björk's body. The animation was constructed from molecular models of DNA and proteins derived from various forms of scientific data such as x-ray crystallography."