Unknown Caller

The Edge explained to Rolling Stone that the idea of this song is that, "the narrator is in an altered state, and his phone starts talking to him."

This song opens with the sound of birdsong, which was recorded live in Fez, Morocco. Bono explained to CNN how U2 ended up there: "Fez is beautiful little city. It's the religious capital of Morocco, and they have a religious music festival there - you know, Sufi singers and Bango drummers from all over the world. I was invited to speak there, and I asked the band - would they be interested in coming along? And surprisingly, they agreed. We set up in a little hotel - they call them riads - and it's a hotel around a courtyard. We set up the band in the courtyard with the square sky over our heads and birds flying in used to come [and] s--t on Larry Mullen's drum kit. He wasn't happy with that."

According to Q magazine, The Edge's long-time guitar tech Dallas Schoo described this tune as "one of Edge's major solos in his life - you won't hear better than that on any other song."