The lyrics were written in five minutes and are derived from U2's experience in Shinjuku. Bono has compared the lyrics to those in U2's 1991 song "Tryin' to Throw Your Arms Around the World", as both depict the nightlife of a city. Lyrics were also inspired by the presence of the yakuza in Shinjuku; the group saw gang members with amputated fingers as punishment for their misbehaviour, which Bono has described as a "very, very surreal" experience. He has said that "Slug" was about avoiding harmful mistakes, stating "we all play with things we shouldn't play with".
